Zimmer launch (outboard)

[Phil Dory]

I plan to build the Zimmer 21' launch - I like the looks and it's big enough for me. I have some experience with wood working and I have built a lapstrake Banks dory.

I don't however have much experience with engines. I would appreciate advice on replacing the inboard diesel in the plans with an 9.9 four-stroke outboard, mounted in a well.

Is that straightforward? Should I keep the rudder? How about the small keel?

[JimD]

Welcome to the forum, Phil. Got some drawing of the design you can post? This the one you mean? http://www.woodenboatstore.com/images/400021.JPG

[donald branscom]

I would keep the keel . You also will need that rudder in the harbor at slow speeds.

[rbgarr]

And you would be travelling at slo-o-o-w speeds with a 9.9 outboard. If it were a ten hp inboard turning a large propeller you may do fine, control- and speed-wise but it's not the same with the smaller outboard propellers and in a well to boot.

For example: the 18' Handy Billy a forum member friend has with a 15 hp engine in a well can move along at about 10 knots at wide open throttle in the best of conditions. It is pretty narrow and medium heavy. Not a boat designed to get up and scoot along on a high plane, though, so that's a good speed for the boat. The TOP HAT design, sort of a 26' version of the Handy Billy with a 50 hp outboard in a well gets along just above 15 knots carrying one person at WOT.

The Zimmer launch probably has more heft at 21' and is less able to approach getting up on a plane. I imagine a 50 hp engine would move her along at 10 knots WOT but it's a pure guess.

I have nothing against moving along at a slower rate. 10 knots is a nice clip IMO and I've travelled at that speed for years. Just today we took a nice long ride (four hours) among the coves and rivers here, even anchoring off and exploring an island. Probably covered twenty miles all told. It's easy to navigate at that speed, steer to avoid lobster pot buoys smoothly and still look around at the sights. It doesn't spook the wildlife so much, either.

[Phil Dory]

Thanks for all your comments - very useful. The plans are those of the 21' 3" Utility Launch by Zimmer available from WB. Here’s a useful pic of the finished boat I found on the web. It’s a nice looking classic little boat, isn’t it? Zimmer really had an eye for lines.

http://www.yachtworld.com/core/listing/displayPhoto.jsp?boat_id=1757389&boatname=22%27+Zimmer+Utility+Launch&photo_revised_date=1186671359000&photo_name=Photo+1&photo=1&url=

The original design calls for a 6-8 hp diesel to push it at half throttle, which is why I thought a 9.9 hp outboard would be enough. From your comments, it seems that a diesel is quite different in quality from an outboard, I 'm guessing in its torque. I have no experience with a diesel. Would a high pitch and larger prop on the outboard help? I could also drop in a 15-20 hp outboard, as you suggest. I don't think the hull would plane eagerly, so any bigger engine would not be needed. I just need enough to push it leisurely as a displacement craft, at 7 statute miles per hour or so.

One concern is that weight would be shifted aft, but a 9.9 hp doesn't strike me as being particularly heavy (102 lbs) and its weight could easily be compensated by putting tanks etc in the fore section. The new 15-20 hp marine outboards from Honda are even lighter (95 lbs).

The reason for an outboard is that the inboard diesel called for in the plans sits smack in the middle of the small cabin and takes up an awful lot of space, relatively speaking. You can see the problem on the picture above. Replacing the mid-ship inboard diesel with an aft outboard four-stroke makes the cabin far more usable, albeit still spartan, while the covered back hatch, in which the outboard would sit, preserves the unique aesthetics of the launch (and keeps it quiet).

Am I being realistic with this conversion?

[JimD]

I assumed you were considering the slower turning big prop/ high thrust outboards such as those from Yamaha, specifically intented for displacement hulls, marketed mainly for sailboats. I think you are being realistic. I had a thread a while back proposing almost exactly the same thing for a Hankinson tug boat. There are such considerations as redistribution of weight but that's not insurmountable. And designing the well to prevent turbulence and loss of boyancy aft caused by cutting a hole in the bottom of your boat, but again, it can be sorted out. I've just built a well in my sailboat which was not designed to have one.

[rbgarr]

Sounds like reasonable plan to me. If the motor needs tilting up in the well keeping the rudder configuration will take some figuring.

Best of luck!

[JimD]

The line drawing taken from yachtworld.

http://www.imagestation.com/picture/sraid225/p5922e37d04fe56d2821b7301eff54ee6/e7c56d48.jpg (javascript:downloadOriginal())

[JimD]

.. If the motor needs tilting up in the well keeping the rudder configuration will take some figuring.

Best of luck!

Agreed. I've just posted a line drawing and from the looks of it the outboard would not have to kick up. It would be protected by the keel. Looks like an near ideal situation. I wish my sailboat had a full keel so I wouldn't have had to give the motor room to kick up.

[rbgarr]

Phil doesn't say where he'd be using the boat, but if it's salt water moored he may want to tilt up the motor to avoid fouling, clogged water intake screen, etc. or at least to be able to scrub it clean from time to time.

[mcdenny]

A high thrust 10 hp outboard would be plenty. The relatively heavy displacement hull won't go more than 7 - 8 mph no matter how much power you have. 2-3 hp would drive it 6 mph in calm water.

A 100 lb motor in the back shouldn't be much of a trim problem. The heavier diesel is also aft of the CB. Put the battery up in the bow if it sits a bit down by the stern.

If you are enclosing the motor you need to figure out how fresh air gets in and exhaust stays out of the motor enclosure. You don't want it to choke on its own fumes in neutral.

If you can arrrange the OB to steer it would be better than a rudder. Single screw inboards with a conventional power-boat size rudder don't steer very well at slow speeds or hardly at all in reverse.

You might aslo consider raising the motor vertically out of the water instead of tilting it up. There are transom jacks made for flats fishing boats that electrically move the motor up & down, some, I think, can travel 8", maybe more. I bet they could make you one with 12 - 14" travel.

By the way there is a WB article (Jan/Feb 2000) about building this exact boat with electric power. I scanned it and sent it to a guy on the Yahoo EB forum. Email me if you'd like a copy.

[pipefitter]

Seems a good plan. And the hydraulic jack( www.bobsmachine.com ) plates raise from 6-8". I saw a boat similar to this with a 7.5 hp auxiliary outboard hanging off the stern and he was able to troll with it. The weight shouldn't be a factor. You may indeed have to add ballast to make up for the missing diesel if the displacement was figured that closely.

[Kermit]

If accomodations concern you, I have two suggestions.

One, choose a different boat. The cabin on this launch is essentially to keep the engine dry and a little of the noise isolated from the cockpit, and to keep a couple of bunks sheltered. It's a day-boat. There's no provision for a potty on board either, if memory serves. That durn engine is right smack in the companionway.

Two, consider a v-drive. There was a Zimmer launch at Port Townsend this year that used such an arrangement, putting the powerplant further aft and opening up the space by a LOT. AND, the owner had moved the helm from forward to a side-steer arangement just ahead of the house to starboard.

Both of these are worth considering if you want to build this boat. Unless you want to consult with someone with design knowledge, I'd stay far away from trying to home-engineer a well for an OB.

The PT boat was coldmolded, by the way. Slick.

I've loved this design for decades. I understand the attraction.

[Phil Dory]

I appreciate all the advice and ideas. I'm now a bit more hesitant to go ahead with the Zimmer launch.

Any suggestions on an alternative design? Basically I'd like a small and trailerable cruiser I can use on the NW coast (Oregon to BC) - good looks count.

[rbgarr]

I appreciate all the advice and ideas. I'm now a bit more hesitant to go ahead with the Zimmer launch.

Any suggestions on an alternative design? Basically I'd like a small and trailerable cruiser I can use on the NW coast (Oregon to BC) - good looks count.

Paul Gartside designed a boat specifically addressing those specs for long distance voyager Bill Hayward: the Wayward design #119 at www.gartsideboats.com (http://www.gartsideboats.com) Hayward made an earlier amazing trip aboard a Gartside pedal boat (#92) http://www.gartsideboats.com/catrow2.php#154 , so I imagine his move to powerboats (and what works) is well considered.

[Phil Dory]

Thanks rbgarr and Kermit and everyone else.

I'm scrambling to learn more about boat design. It's a fascinating field, albeit somewhat confusing for a beginner.

How flexible are boat designs? If one compares the Redwing skiff with the Zimmer launch, both are about the same length (the Redwing has plans from 18 to 24') and beam, but the launch is round bottomed with inboard while the skiff is flat with an outboard.

Are they equally seaworthy? Maybe I'm naive, but where do you find answers to these questions?

Does making a change, such as from inboard to outboard, or any change of that scope (adding berths etc), really require input from a designer? Do builders generally strictly follow plans?

I understand that one should be careful here, given that one's life may depend on the design, but what is the common wisdom on how much flexibility one can take with designs?

[rbgarr]

I'd say the common wisdom with boat designs for a novice or first time owner is find one by an experienced designer, see if you can go aboard or even get a ride on one that you're interested in, and ask the designer about making changes. Much like designing a house... that will probably cost more per pound, be used purely for pleasure (so it better work well to be fun!), be much more costly per hour of use, must float, maneuver and be attractive to a wide enough market that you'll be able to sell at a later date. Good designers coordinate all these requirements in a compromise that can suit and let you know when they irretrievably conflict at a reasonable price. A novice is almost sure to end up in a corner with problems that are expensive, discouraging and like the proverbial 'tar baby', yours for a long time..

[paladin]

I had a few conversations with Nels Zimmer in the few years before he passed and this boat was discussed often. I thought about a 30 foot version of it for a long time. It's a nice comfortable proper craft.

[Phil Dory]

Paladin, would you be so kind to recall for us some of the things that Zimmer said about his launch's design? I've seen quite a few photos of the boat on the web and I find it a very elegant design. I know there are a few afloat on the west coast. I hope to actually see one soon, even board it.

[mcdenny]

The Zimmmer launch is much heavier than a Redwing and will have a more gentle motion in waves, will take more power to go the same speed in calm water. It will punch through a head sea where as the Redwing will pound that flat bottom.

Launch would cost at least 2x to build (time plus $$)

They are quite different boats. Neither is really suited to big water on a windy day.