Offshore motor vessels

[Alan D. Hyde]

We've touched on this before in terms of long-distance voyaging (Beebe, etc.), but what about coastal cruising?

There've been some trawler yachts discussed in various threads, and some fairly slow, heavy displacement boats talked about, but I've not seen a lot about sea-keeping characteristics of planing offshore boats.

The PTs in the Pacific successfully weathered some pretty wicked storms in WWII, and several lapstrake models have good reputations as sea boats. Bertram step hull models did pretty well in 10" waves running Miami-Nassau.

What do people think is the best choice for an offshore powerboat? Do two engines really provide that much of a safety margin? I personally think a self-bailing cockpit with adequate washports is a good idea. A steadying sail could make sense too.

I would agree with the comment on another thread that most pleasure power vessels don't go far offshore much. Cost of fuel is one factor, but, if we can rationize that (well, winches are expensive, and new sails aren't cheap...) what's the best boat in the affordable by ordinary people (30-40 foot) range? Thoughts? Experience?

Alan

[ 04-12-2002, 03:52 PM: Message edited by: Alan D. Hyde ]

[Donn]

Originally posted by Alan D. Hyde:
... Bertram step hull models did pretty well in 10" waves running Miami-Nassau....
AlanAlan...those 10" waves can be real killers! :D

Seriously, though...I've been 75 miles offshore (which is half my range) and weathered some pretty heady seas. I can't outrun bad weather, but I can certainly throw the hook or a sea-anchor and keep buttoned up with my bow to the seas. I imagine a good planing hull could do the same thing. I can run into 10-12' waves with relative comfort, but if my destination is in the opposite direction, I have to hunker down and wait it out. I've spent many hours running ahead of 6-10 footers on Lake Erie, in a fast outboard...there wasn't any constant planing, but having the speed to ride the seas got us home every time.

I have twins, so I'm biased, but I have redundancy in every operational system in the boat. I just feel better knowing that I have backup.

I doubt that there are any 30' sailboats which could deal any better with heavy weather than my ole stinkpot.

[Alan D. Hyde]

Donn, I talked to Dick once, and he wrote me a letter about a year before he died.

According to him, slamming through those waves in Brave Mopie would "shake the fillings out of your teeth."

From experience in smaller boats at lower speeds, I believe him.

Alan

[gary porter]

Alan, The Tolman skiff is used quit well for offshore and coastal work. check out www.foggybayboats.com (http://www.foggybayboats.com) click on the map and then go to the "Skippers Tales" Dick Bird has had quite a few great adventures in this boat. Renn's page is www.xyz.net/~mgrt/ (http://www.xyz.net/~mgrt/) (thats a tilde mark before the mgrt) You can also see several other examples including mine on www.fishyfish.com/tolmanskiff.html (http://www.fishyfish.com/tolmanskiff.html) There are a great many of these up here and they have a really great reputation as being dry and seaworthy. smile.gif

[Tom Lathrop]

Alan,

PT boats have weathered some storms but WWII PT's were far from good sea boats. They were fast in easy water, as were the British counterparts, but the German E boats were much better at sea than either and faster in the rough stuff.

Being on board a small fast boat while trying to get back from the Gulf Stream and outrun a storm is not something most will like to repeat very often. Personally, if I had to do that in a powerboat, I'd look at either a multihull or one of the new wavepiercer monohulls. I doubt that either can be made as an adequate offshore cruiser at 30 feet.

Probably the best bet in your size range would be a semi displacement hull if you want to go faster than hull speed.

[plimsol]

Alan,

If I were planning to go offshore in a powerboat, I would not choose a planning hull form. I would like some draft and an easy motion. Take a long hard look at the West Coast Salmon Trollers. They were meant to go out and stayout. They would range from the Gulf of Alaska to half-way to Hawaii.
Ed Monk and William Garden designed a series of Troller Yachts in the 1950's and 60's that evolved from their commercial designs. Both have written about subject in Sea Magazine and several articles in Yachting. West Coast Trollers are almost exclusively single screw. The yachts occasionally would have take home drives off the generator.

Engine reliablity is largely a function of owner maintenace and systems knowledge. If the owner cannot keep the fuel clean and manage it, a second engine is not going to provide any additional safety. I believe this is also true in airplanes.

I will keep this rant short, what Madison Avenue calls a "Trawler Yacht" is not. If it can plane its not, If it takes 600 hp to do 15 knots its not, good advertizing copy does not make a vessel a good seakeeper. Finally, the "Trawler Yacht " is a bastardization of Monk and Garden's "Troller Yacht" design ideas, at least on the West Coast.

[Scott Rosen]

Alan,

How fast do you want to go? If you're content to do under 10 knots, then a good motorsailer in the 30 to 40 foot range can handle just about any offshore conditions. The advantage of a motorsailer over a power yacht is that the motorsailer can stay underway when just about any power boat would have to heave to. Another advange is the increased range you get by having the sails.

[DesignByBird]

One of the more interesting questions I’ve seen, nice one Alan.. for my penny’s worth as a designer and a user, I would point out that serious high speed offshore boats have sprung seating, crash helmets, and good harnesses.. That should give a clue.!

PT boats were designed for a job ~ ‘get in undetected – get out fast !!’ They chose petrol, rather than the more reliable diesel, for that exact reason.., Getting out with your hide was more important than the getting out with what you had for breakfast..!! and that related to range making speed and speed of manoeuvrability !

Next economy ; Getting a vessel up on plane takes a lot of power &/or low weight, like driving a car at 75mph gets you there fast, but driving smoothly at 50mph is almost twice as economical. Friction is one big thing, lifting (defying gravity) a boat onto a plane is another. Naturally once there it reduces friction, but then every wave it hits is like a brick wall in comparison to the resistance of going through the air. This pounding is what makes planning power boats so exhausting.. exhausting equates to tiredness.. and tiredness (fatigue) leads to mistakes and errors of judgement..

By and by.., this pounding (rather than riding with the seas) means that the vessel has to be super tough, (not only against high-speed impact of debris, but) to prevent their backs breaking, their sides and therefore the joints from panting and cracking open. Strength means either high cost materials &/or heavier weights. Heavier weights mean more power.. more fuel.. more weight.. more strength.. more power.. and so on..

Most import for cruising capability is comfort.., and that equates to the ability to keep going safely.. A planing hull has shallow vee aft and hard chines which is buoyancy at the extreme corners.., and this buoyancy rises to every wave.. (distance from centre equates to leverage, where even a small wave’s buoyancy has the power to rock a boat ) and that means harsh, abrupt, uncomfortable motion (un-dampened). Rapid up & down, up & down.. That is really nauseating.. Sit on any race committee powerboat at anchor for a few hours and you’d wish you were sitting on a sailing boat with a round hull sections (which doesn’t ride to cross seas) and a keel (which provides damping to the motion).

Finally weight is crucial.. On a cruising boat, the requirement is usually to carry a lot of provision, plus a host of longer term comforts (appliances and ‘padding’). Planing boat hull-forms are much less efficient through the water at displacement speeds (and when heavily laden). So if you (&/or your wife) are likely to laden the vessel for that dream cruise.., down don’t go for a planing hull, otherwise you will pay heavily for it in fuel.

So, what’s your criteria, high speed to pop around a headland and sit in a marina for shelter, or the (relative) comfort and durability for a longer period of time - greater range ? Bottom line is that yes – planing hull forms can be seaworthy, but rarely will they be as much so (too many other compromises), or as comfortable, as a displacement hull-form ~ cradled into (rather than bobbing about on) the water.

One or two motors ?.., in my opinion, the motors themselves are generally reliable as long as regularly maintained, whereas the cooling, fuel supply and systems are the problem. Personally I would use that cost value to make everything else fail proof.. that will take another page to cover !!. Though you may consider twin drives.. (also easier for manoeuvring and better for shoal draft). Oh yes, and don’t neglect to invest in decent ground (anchoring and drogues) tackle.., it may save someone’s life.

That’s All Folks !! (for now)..

Hope it helps.., Pete

[Dave Fleming]

Alan, on the off chance you are not familiar with what is being referred to as:
Troller Yacht, I am attaching a photo of a Wm. Garden design currently for sale in the classifieds of WB. Garden has been designing similar for many years and they are popular on the West Coast of the US and British Columbia. They truly are based on a fisherman type and while usually 'hell for stout', they do need 'flopper stoppers' to smooth out the ride, if ya folla. Garden's design books show at least one of this type and others that are comfortable going offshore. Bye comfortable I am not talking in particular about smooth ride but rather a safe well designed vessel.

http://www.imagestation.com/picture/sraid18/p9be3656af97d50d105d6508c6d0ede70/fdcf3f36.jpg

[ 04-13-2002, 02:32 PM: Message edited by: Dave Fleming ]

[Donn]

That's a pretty boat! But I must be blind...can't find the listing.

But I found 6 or 8 others I wouldn't mind having! :D

[ 04-13-2002, 02:59 PM: Message edited by: donnwest ]

[Donn]

Damn! My back pages are starting to stick together! I've got 80' of empty bulkhead threatening to eat a hole in my IRA. Then, of course, there would be the constant argument among the boats for a spot in the shed.

[Alan D. Hyde]

Thanks for the many astute observations; I am learning slowly, but I AM learning...

The tension between speed and the seaworthiness of hull forms and displacements (i.e., easy motion vs. bobbing cork) is particularly ironic since speed itself can arguably be a major factor in seaworthiness, by enabling the vessel to avoid a major storm system.

There are design factors that can reduce the slamming at speed, but not eliminate it. As several have noted, getting power without too much weight is problematic. I wonder if anyone has done a turbo-electric drive in a boat of this size?

Of course, all small boat design involves trade-offs, but it seems to me that small offshore power vessels don't (right now) emerge from this process as well as the best similarly-sized sailboats have.

And we haven't even gotten into stability...

Alan

[Donn]

I don't think you can get a much rounder chine boat than mine.

Something to think about with the single/twin configuration. Both my engines get exactly the same hours, and exactly the same maintenance. They each have their own gas tank, and they each have their own battery/starter, etc. There is no crossover between the fuel tanks. The boat is driveable on either engine, but not much fun for cruising. On both engines, with Aetna tachs to synch them (I'm getting better at hearing the synch), I get 3GPH at cruise of 10. If any part of either drive system goes bad, I can still keep my bow into the seas.

Don't even talk to me about the agility of a twin screw vs. a single screw. I can walk this tub thru the tightest anchorage or marina without touching the wheel. She'll turn 360 in 31 feet, and she's 30' long.

I NEVER fill both tanks at the same unknown fuel dock...got too much bad diesel to ever do that again. I almost always buy my fuel ashore, and fill her myself. There are a few trustworthy docks around here, but when I take her somewhere else, I'm very careful about fuel. Each engine has 2 fuel filters, the second finer than the first.

10-15KTS is not sufficient speed to outrun a heavy following sea, and I don't try. I'd rather wait for the surface to settle down, or change course. There are times when the only way into the inlet is with huge folloing seas, and I have two 4 inch scuppers in the transom to drain the cockpit, and the biggest pump Rule makes sitting back there just in case. Even with almost 3 feet of transom above the waterline, I still take on alot of H2O in a hard following sea.

Soft chine, trimmed well, and an abundance of caution...a downeast hull will get you home...eventually.

[swingking]

Catamaran Power-Boats can be designed for high speed or long range or a combination of either. Catamaran Trawlers are generally designed to achieve cruising speeds of up to 15-17 Knots and have very long range at normal Trawler speeds of 8-10 knots.
Catamaran Trawlers are a relatively recent development. Benefits include: Longer range for a given fuel consumption.

Fountaine Pajot
http://www.bayacht.com/trawler.htm

TrawlerCat Marine Island Hopper 43'
http://www.trawlercatmarine.com/islandhop43.html

PDQ MV 32 - Passagemaker
http://www.pdqyachts.com/theCats/mv32/mv32Intro.html

[Donn]

Alan...this may be what you're looking for:

http://www.msdieselduck.com/images/dduck1.jpg

http://www.msdieselduck.com/

The Troller Yacht Book : A Powerboater's Guide to Crossing Oceans
by George Buehler

[ 04-17-2002, 03:40 PM: Message edited by: donnwest ]

[Donn]

No Dave... This is a butt ugly boat:

http://www.noblesmarine.com/boats/2000maxum2800.jpg

[Alan D. Hyde]

An interesting link, Donn. Thanks.

Alan

[swingking]

The poorman's trawler that I like is Buehler's Dory hulled Pilgrim 44.
With 7 knots at .18 gph calm and off-weather conditions.

http://www.georgebuehler.com/Pilgrim.html

http://www.georgebuehler.com/georgeimages/Pilgrim%20outboard%20version.jpg

Mat

[RGM]

I've been contemplating a response to this thread for a little while now. So here's my $0.02 worth. First off, Alan, where are you going cruising? I see that your hailing port is Indianapolis. Will you be on the East coast, West coast or South coast? Is speed essential? If I was looking for the most bang for the buck in terms of an offshore cruising "powerboat" I would opt for one of the commercial designs that are popular in the North Pacific. Along the lines described previously by Plimsol. These would be salmon/tuna trollers, longliners and salmon seiners. Salmon gillnetters are nice but they tend to be a little smaller. Commercial fishing is depressed right now around here and there isn't any relief in sight. Fish farming has adversely impacted the market for wild salmon. I hear that someone somewhere is having success with farming halibut and black cod also. The North Pacific long line fleet will probably go the way of the salmon fisherman. In other words, there are some great deals on boats in the PNW these days and in the future. Probably more so in Canada right now. The exchange rate is very favorable to U.S. buyers. Check out wood "unlicensed fishing boats" at www.frenchcreekboatsales.com (http://www.frenchcreekboatsales.com) . Fellow forumite Terry Etapa is doing a yacht conversion on an ex-Canadian salmon troller. He has a website and posts his progress. Do a search for him/it and check that out. Anyway, there's a few thoughts from an ex-Alaskan fisherman that may interest you or some other like minded forumites.

[ 04-17-2002, 11:56 PM: Message edited by: RGM ]

[Alan D. Hyde]

That's a good website, RGM. Thanks.

I don't know much about PNW boats. If I had to choose a workboat from what I know by my own experience, I would lean towards a Maine lobsterboat, maybe a Beals Island type. But there's a lot of experience out there that I haven't had...

Swingking, I wonder how many "dory hulls" have been built? I'd worry that the flat bottom would slam under some conditions, and that it wouldn't let the weight be put as low as many other hull types.

I've been told that a good ocean-going tug does surprisingly well in bad weather, but I've never been on one, so I don't know how much of that comment is loyalty to the vessel versus fact.

In the world of workboats, aluminum construction seems to command a premium, and wood is discounted, with steel on the higher end of in-between (I didn't look at the glass part of RGM's link).

Alan

[johnw]

I grew up in Maine and admire lobster boats. They go out in the morning and come back at night, and don't stay out in a gale if they can help it. Lobsters are caught in the rocks near the shore. Troller have to stay out, they fish too far from home to get into port when the weather makes up. They have the range and the seakeeping ability to be real offshore boats.

[swingking]

A few guys on the following list had started Pilgrim 44s.

http://groups.yahoo.com/group/backyard-boatbuilding/

I am thinking that the small 7.5' waterline beam would help keep the Pilgrim low in the water. I would be tempted to have some extra seawater ballast used only for bad conditions. Buehler's plans in "Backyard Building" call for very strong construction.

Mat

[cmorse]

Speaking of converted West Coast fishing trollers, which Buehler and others have sung praises about, there are a number of boats being offered as conversions or conversion possibilities from a number of dealers/builders on the West Coast. Someone has already referred to French Creek in BC and Sam Devlin has just converted one and is in the process of completing another one. This link has the one he just finished. www.devlinboat.com/usedboats.htm (http://www.devlinboat.com/usedboats.htm)

They are beauties, in my opinion but you really have to be careful on choosing one for conversion. Many of the fisherman have not been able to afford upkeep over the years so the low priced ones are priced that way for a reason many times. Just depends on what type of project you want to invest in...

[cmorse]

Speaking of converted West Coast fishing trollers, which Buehler and others have sung praises about, there are a number of boats being offered as conversions or conversion possibilities from a number of dealers/builders on the West Coast. Someone has already referred to French Creek in BC and Sam Devlin has just converted one and is in the process of completing another one. This link has the one he just finished. www.devlinboat.com/usedboats.htm (http://www.devlinboat.com/usedboats.htm)

They are beauties, in my opinion but you really have to be careful on choosing one for conversion. Many of the fisherman have not been able to afford upkeep over the years so the low priced ones are priced that way for a reason many times. Just depends on what type of project you want to invest in...

[Ross M]

Hello, folks. Longtime reader, infrequent contributor.

This thread has delivered a lot of high quality debate, IMHO. Thanks in particular to DesignByBird for explaining the adverse effect hard chines have on motion.

A question: What is the general consensus regarding Seabright Skiff style hulls? Dave Gerr’s “Nature of Boats” seems to hold this form in very high regard, and he delivers some pretty persuasive argument as to why:

The box keel apparently allows low CG, provides good seakeeping and the ability to take ground without damage. Further, the large flat keel allows semi-planing speeds while retaining the seakindliness of rounded chines.

I have found little to contradict Mr. Gerr, any thoughts on why the form seems to be relatively rare?

Ross McDonough

[gary porter]

cmorse, The "Lean-To" is a beautiful boat, took a walk through it last fall at Port Townsend. I think anyone would love to have her. I'd like to see more of the old fishing boats converted this way rather than just rotting as yard derelicts. They can take alot of time and money but the original purchase of the hull can be quite low. The fisheries are depressed right now and alot of these old boats are coming up on the market. They're a good deal if you like to work on old boats and I think everyone should have at least one. "Lets save em" Doesn't quite fit the planing hull part of the original question but a great boat anyway. smile.gif

[Tom Lathrop]

Ross,

The comment about motion comfort and round versus hard chineed hulls sounds good but does not stack up to experience. For instance, our local dinghy club uses a 26 foot ex-Navy whaleboat for a race committee boat. The motion of this heavy, round bottom beast at anchor in even mild waves is enough to drive you batty. In the wake of large passing powerboats in the ICW, it is downright dangerous if one does not hang on to something and gather up all loose gear. That is, it was that way until we added some Flopper Stopper cones on each side. Now it is at least bearable if not comfortable. Likewise the flying bridge of a friend's round hull Cape Dory powerboat is uncomfortable at anchor in waves.

On the other hand my 24 foot hard chine powerboat is much more comfortable at anchor than either. Even beam-on to the seas it has far less violent motion than the whaleboat when head to the waves. Other hard chine "trawler" hulls that I've used as committee boats are also far better at anchor in waves than any round bottom hull.

You have been misinformed. The sailboat at anchor has a much longer roll period because of the large moment of inertia of the deep keel and the mast and rigging up high, not because it is round hulled. All else being equal, the hard chine has a quicker motion to waves, but this does not mean that it is less comfortable than a round hull that may take slower but far deeper rolls. Of course we are not talking about extreme conditions here.

[ 04-26-2002, 02:22 PM: Message edited by: Tom Lathrop ]

[Terry Etapa]

Since RGM mentioned my project, I'll post the URL.

http://www.home.earthlink.net/~tetapa

I haven't updated the site since January. Right now I'm putting in my fresh water system. Once those photos are developed, I'll do and update.

Terry

[ 04-25-2002, 08:23 PM: Message edited by: Terry Etapa ]

[Ian McColgin]

William Garden designed a nice dory sided unit of about 60' and very narrow with low power. I dream about this sort of boat when I realize that after I rebuild Grana I'll have a nice 20hp Deutz in need of a home, and when I'm not thinking realisticly about actual time and ambition.

I think Dave Garr has a more off-shore like version of the same concept.

Narrow lines. Low total profile. Simple lay-out. Both boats fully able off-shore yet they can next up on a sand bar in a wee tickle.

Keep her simple. Keep her cheap. Go far. It's easy to tank for a 3000 mile range if you drink less than a gallon an hour.

[Ross M]

Tom: Thanks for relating your experience. BTW, I think "Liz" is an exceptionally handsome power boat.

[Matt Middleton]

Here's a site with a little bit of discussion on motion and stability. He's got some nice designs, as well.
http://www.kastenmarine.com/index.htm
Matt

[Mike Keers]

Alan, all,
I've been following this thread with some interest, because as a life-long sailor, I'm building my first powerboat, the Stambaugh-designed Puffin 28 diesel cruiser. It's a displacement hull, altho' I guess the actual displacement of 6500# puts it more in the 'semi' category, compared to some 'trawler yotts'.

My wife has been tiring of sailing, and keeps saying 'it would be nice to just turn the key and go where you want to go for a change'. After a 3200 mile solo passage from Mexico to Hawaii a coupla years ago, I thought it might be nice to sit inside in comfort and watch the scenery pass by at 7 knots for a change too.

I plan to use this for coastal cruising, but I wanted some rough water ability, as my cruising grounds include the Sea of Cortez, and it can get pretty rough down there at times. Also thinking of doing the Inside Passage from the Pacific Northwet up to Alaska.

Anyway, the reason I held off writing was because I've been trying to hunt up a back issue of "Boatbuilder" magazine, that has an article by Dave Gerr on choosing a motorcruiser. I found the issue, and it's the November/December 2001 issue. If you can lay your hands on it, there's much thuoght provoking stuff--not so much on stabilty and motion (I think Beebe's "Voyaging Under Power" is the seminal bible of power voyaging), but Gerr's article focuses on speed versus fuel economy versus displacement. Gerr's personal preference for coastal use is for fast motorcruisers, his argument being you can get the most bang for your buck if you're doing the normal type of coastal stuff, not living aboard and crossing oceans. His point is your radius of operation is increased in a given time period.

The interesting part of the article (to me) was the comparison between five different designs, all more or less the same 'real' size considering displacement. The boats are perhaps on the large size, running from 42 to 48 feet, and ranging from 28,000# up to 52,000# displacement.

What is eye-opening is the breakdown of cruising and top speed versus fuel economy. While the most economical boat, the 42 foot 'trawler' (a misnomer according to Beebe) uses only 2.7 gallons per hour to cruise at 7.8 knots, the high-speed planing boat, a 44-footer, uses 27.2 GPH at a cruising speed of 28 knots. The actual miles per gallon show these same two boats, the 42-foot 'slow' cruiser gets 2.94 MPG, while the 44-foot high-speed boat gets 1.03 MPG.

On the other hand, the fast boat can get to a destination 28 miles away in one hour of crusing time, while the slower boat will take over 3 hours.

I guess the whole point of the article is to give food for thought about how you plan to use the boat, and where on the curve your time versus how much you're willing to spend on fuel.

My Puffin, which I chose for economy, will cruise forever at about 7 knots, using less than 3/4 GPH. I'll be running a Yanmar 3HM35, spinning an 18" prop very slowly. Since the boat is semi-diplacement, it may actually be able to top out at about 9 knots, flat out, for short periods. After coming from a 29-foot sailboat that cruised at about 5 knots and took a gale to break 7 knots, sitting in a pilothouse in my slippers sipping coffee (a la Beebe) putting along at 7 knots will be blindingly fast. :D

[Ken Hall]

Going back to the question of one engine or two, let me put in my oar for two if you can afford it. Apart from the nice margin of safety that 100% redundancy offers, two engines and two screws makes a world of difference in maneuvering in restricted places like marinas (I'm sure a couple of the old salts will spit tar at me for suggesting that two engines are necessary for hoicking a 13-ton woody around in a marina, but if it weren't for people like me who would you make fun of? ;) ). Either twin engines and twin screws, or a bow thruster, but it'd be hard to limp to a landfall on a bow thruster.

'Course, it does use more fuel, but if you get a boat with diesels instead of gassers and keep your speed down it ain't so bad. May dad's old '48 Matthews sedan cruiser was twin 1962 Chrysler 413s (wedge-head big blocks, replacing the original Packard straight 8s), and apart from the fuel consumption she was a sweetheart.

[ 04-30-2002, 09:32 AM: Message edited by: Ken Hall ]

[Jamaica Mike]

Spent a bunch of time in a 27' Monterey hulled salmon troller. This is a wooden double ended troller design, which was built in 1937 by a builder on SF Bay.

With single Chrysler Crown 6 we went all over the west coast and lived on board for 10 to 14 days at a time. It is a boat design that is easy to be in at sea, and I have often thought how fine it would be to convert one to a cruiser.

JAM

[Wiley Baggins]

This is just the sort of post to turn an infrequent lurker into a full-fledged poster. There is something magical about sitting around the virtual stove talking designs. In this context it's a chance to help someone, while indulging in the desire to say "sure that's a great boat, but what about..."

In that spirit, in order of their publication in WB, what about these.

1. Powerboats (~25'-~57') from Winthrop Warners pen(cil)-WB 75

2. Montery-Type Cruiser (~33') by Al Mason-WB 108

3. Kettenburg 38' commercial fishing boat-WB 116

[DesignByBird]

Tom, On the whole I wouldn’t disagree with you regarding round hulls, but in that particular text I was specifically considering the cause of the roll, rather than the applications that we use to control it - after it has started.

As you read, I did make note of the keel (lateral resistance to damping) and the ballast (kinetic resistance to rapid changes of course or direction) in anticipation of the question of damping and therefore (just one aspect of) control.

Bottom line is that a round hull will not start to roll – (and yes you are correct) nor will it stop rolling - as readily / abruptly as the hard chined shallow-vee - planing ‘PT boat’ type hulls (the question asked !) and as such the motion is deemed to be less harsh.

The offshore supply vessels, exploration and research vessels, and troller yachts which we designed and built ‘way down south..,
http://www.fgh.com/HalterMarine/HalterMarine.htm
usually had double chines. Arguably this was the better compromise in Seaworthiness and economy because the hard chines (of a planing hull) are cut off - which reduces rising to the seas, and the chines (around 125 deg.s) give considerably more damping than any true round section.

However, (because there is always a however !) on smaller boats, wave impact (slamming) onto the flat between chines can be a worse experience than roll. Perhaps this is one of the reasons that lifeboats are traditionally and still made round bilge – but with a hefty keel timber to dampen roll ??

Inertia / mass / displacement obviously makes a huge impact on the quickness of motion and the damping needed, and that is just one of the reasons that empty work boats don’t necessarily make good yachts ! Your ex-navy whaleboat being used for race committee work is proof enough that you can’t simply take a design intended to do one job and satisfactorily use it for another. Like most powerboats, when was a whaleboat ever intended just to sit there !!??

I am Not wishing to argue, nor to 'misinform' -just to clarify my intent.

Regards, Pete.

[Albie]

Donn-go to your room for showing that picture of that thing!

[siberianswampdonkey]

Well how about glenl's Bandido its offshore 30' long and it says its 50knot capable :eek:

[Tar Devil]

A 29' Bartender, perhaps?

(26' version)
http://www.boat-links.com/PT/PT2001/Bartender.jpg

Later,

Phil

[siberianswampdonkey]

What's the big tug like boat in the backround?

[Dave Fleming]

What's the big tug like boat in the backround? With tongue firmly in cheek....
I'm just guessin' mind ye but, I would say a wooden tugboat. Named Katathadin or similar.

Looks like the photo was taken at some wooden boat festival in the Pac No West

[ 06-18-2003, 07:55 PM: Message edited by: Dave Fleming ]

[Alan D. Hyde]

Dave, :D :D :D

Alan

[Dave Fleming]

Well Alan, I do hope that the Siberianxxx, takes the comment in the jocular spirit it was posted in, sigh.

[siberianswampdonkey]

Don't worry dave. :D :D :D :D :D :D

[David N.]

One of the boat's , I have been looking at is a , Van De stadt ( sp ) , it is the only power power boat they have ever designed , it is a 38' they call a " green " boat , but then it is an aluminum hull , still it is rather nice looking .