10-20 knots boatspeed

[imported_Peter K]

Is there a hole in the range of useful, achievable boatspeeds ?
Motor that is.
As I've looked at designs that might replace my (aargh) aluminium 17' skiff, it looks like you can have either a planing craft or a displacement one.
I want a boat that is happy to run at 10-20 knots, and therefore manage a nasty chop at a suitable speed.
It needs to be no more than 20 or so feet long and capable of living on a trailer, and towable by a car, not a beast of a truck.
Preferably outboard powered.
Buildable by an amateur.
Preferably not stitch and glue.
The planing boats will not operate between 10 - 20 knots (mine wont any way) without using inordinate amounts of fuel and displaying a bad attitude, and handling badly.
The displacement boats will not go over 10-12 knots, - I know about the relationship between waterline length and speed but I cant afford a displacement craft long enough to go 18 knots.
I have heard of, but never seen a semi displacement boat.
Well, maybe I have but I didn't know it.
Could they fulfil my requirements ?
Can they cruise at 18 or so knots, and handle rough water ?
Does any one have any experience of such craft ?
Any suggestions ?

[ 06-10-2003, 08:21 AM: Message edited by: Peter K ]

[Lazy Jack]

Interesting question. Off the cuff I would guess that the only way to defeat the catch-22 that you present is to step away from the conventional hull types that are governed by the standard formula for hull speed. I know that as a hull gets long and skinny, it's 'hull speed' is no longer governed by the standard calculation (I have no idea of what the formula would be or what elements it would contain) For example multihulls move much faster than their length would predict without planing. If you are restricted to 20' in length a powered monohull would resemble a powered rowing shell! Sounds like a powered multi-hull is the way out of the box unless you can find a way to go longer than 20'. I'll be watching for some input from others. This is interesting.

By the way, in the context of a 20 foot boat going 18 knots what does 'rough water' mean?

[ 06-10-2003, 08:39 AM: Message edited by: Lazy Jack ]

[John Bell]

Two designs that come to mind are Harry Bryan's 'Handy Billy' and John Atkin's 'Ninigret'.

Handy Billy is batten seamed carvel planking over sawn frames, either 18 or 21 feet LOA, 15 to 40 HP outboard powered.

http://www.nwboatschool.org/images/Handy_Billy_1.gif

Ninigret is plywood over sawn frames, 22 feet loa, 30 to 40 HP outboard powered.

http://jmbell.home.mindspring.com/images/ninigret.jpg

And finally, tossing in a stitch and glue alternative, Jacques Merten's composite plywood interpretataion of Ninigret, the 21' Nina.

http://www.bateau.com/images/boatpics/LB22_Bow_350.jpg

Each of these boats are advertised to cruise at 15-18 knots with the specified power. All are semi-displacement hulls, reputed to handle well in choppy water.

I'd be happy with any one of these.

[ 06-10-2003, 09:18 AM: Message edited by: John Bell ]

[Scott Rosen]

I think the short answer is that you can't have your cake and eat it too. If you want a boat not more than 20 feet loa that will travel at speeds of up to 20 knots, you will need a planing hull and lots of power to get and keep it on a plane.

The flatter the bottom (think Boston Whaler), the less power it will take to get on to a plane. However, you will lose the ability to handle a chop or steep seas with comfort and safety.

The deep-v bottoms (think Grady-White) are very stable and seaworthy in a chop or steep sea, but they require a lot more power to get them on a plane.

It's all about compromise. Speed, comfort, fuel economy. You can have any two; but not all three.

[Donn]

Sounds like a powered multi-hull is the way out of the box Yep. Do plans exist for wooden power catamarans? I've never seen a wooden one, but I can tell you from experience that there is no more stable, seaworthy, fast and fuel-efficient fiberglass or aluminum power boat than the power cats. They aren't real pretty, but they certainly do work well.

[ErikH]

Hmm. What about the Pulsifer Hampton, or something like it? It's reasonably speedy, nice looking, small engine...

[Ian McColgin]

Pete Culler's OB skiffs like the Osprey will fill that hole very nicely.

G'luck

[Tom Lathrop]

It is possible to design a boat that will do what you want and run comfortably and efficiently in the 10 to 20 mph range. Semi displacement types like the Handy Billy can do the low/middle part of that range if they are long and narrow enough and watch their weight. Most semi displacement boats are too heavy for low power though and push a lot of water if you want to hit 20 or above.

The other way to do this is to design a low weight planing hull, with a proper bottom design, that can extend the planing range down to 10 mph. That is a much rarer bird and there are few that can do it. Such a boat will not be good much above 25-30 mph, which may explain why so few are built. As a boat salesman told me, you can't have too much power or go too fast or be too streamlined or have too many dark windows for the planing boat market.

As far as I know, if you want a boat that will cruise economically and comfortable in the 10-20 mph range, you will have to build it yourself, or have it built.

[capt jake]

As far as I know, if you want a boat that will cruise economically and comfortable in the 10-20 mph range, you will have to build it yourself, or have it built.
As I intend to! ;)

[seafox61]

you might want to look at Phil Bolgers sneekeasy. their are some open versions that are even lighter than the origional plans. the flat bottom spreads the weight so that it does not have to push a lot of water aside and actually planes at low speed power. it is longer than 20 feet at 26 foot but its light weight means it can be towed by your vehicle of choice. if you want a cabin look at Mr Bolgers Tennessee. in the origional artical he pictue it beng pulled by a car

out of the range of our idea the wyoming was a double scale sneekeasy for a 52 foot low power cruser and one fellow sugested doubling that hull to make a 102 foot personal aircraft carrior
jeffery

[TomRobb]

I'd second the Bolger thought, although perhaps not the Tennessee, a box-boat, in particular. It seems to me that Bolger has designed at least a few boats like what you want. I'd FAX or write him/them - Bolger & Friends. He's creative, accessable, capable of really lovely boats (if you want that), and has been there and made his own t-shirt :D

[mmd]

Something like this "mini Cape Islander" (maybe without the telephone booth wheelhouse :D ) might fit the bill. This is a Rosborough 18 built of the "other stuff", but the type is readily built in strip plank. This one is fitted with an Evinrude 50 hp outboard, which pobably moves it along at 20-25 knots. Some fools put 150-hp engines on these and get 'em going near to 40 knots or so, but steerage must be pretty squirrely at that speed. My sister's father-in-law had one for years (no wheelhouse, just an 6-ft cuddy-cabin with a windscreen atop) that he ran with a 40-hp Mercury, and we'd run at 18-20 knots wide open and troll comfortably all day at 6-8 knots. This was in the Atlantic Ocean off of Lunenburg, not sheltered bays or rivers. Good little boats, these. This one is offered at CDN$14,000 (USD$10,350) complete with trailer, motor, lifering & lifejackets, depthsounder, compass, fire extinguisher, and mooring gear.

http://newimages.yachtworld.com/1/0/8/5/3/1085318_1.jpg

[Alan D. Hyde]

Here you go :D :D :D

(with compliments to mmd: see his "new boat porn" post)

http://www.imagestation.com/picture/sraid65/pc2aaf17d5f411676de9a751ab5ba848b/fbf4abee.jpg

Alan