How difficult to convert this engine to variable speed?

Something like that, yes.

And having done it that way, you would have some 150 lbs or so saved above WL, then a sandwich made house would be within technical possibilities.
Due to the fact that there is no Atkin left to revise the plans, who will do that? I do´nt feel comfortable without.

Did I understand the post above right? The engine is´nt available any longer?

Regards
Richard

 

The engine is available - TowmanDoug was suggesting an even less expensive alternative - a Perkins - which is, sadly, out of stock.

As for stability; after the boat itself was built, I would do a mock up of the center console/enclosure to simulate the height and weight and do some sea trials before I built the real thing.

Another thing to consider: Atkin provides 2 sets of lines with the plans - one hull designed for 9-10 knots, the other for up to 16 knots.
I assume that the faster hull has less upsweep to the chines aft, providing more bearing and bottom for prop thrust so she doesn't dig a hole. This has me wondering if the faster hull would also provide more initial and reserve stability.

Methinks it's time to order the plans and find out!

 

Nothing can beat a empirical test....................

Due to your engine choice (and economy), there will be only one choice left, which one to build!?

What was it 55$ or so. I think that is a good and relatively cheap start.

Regards
Richard

 

Better hull choices?

Perhaps either of these two would be more reasonable for the power:

Devlin Dipper. I would lengthen this hull 2-3' for more fishing space, which I think would also be necessary for an inboard installation:
http://www.devlinboat.com/dipper.htm

Atkin Surprise. I might add 1' to this one, and move the low cabin forward 2'. Then I could add windshield to the aft edge of the low cabin, with some kind of foldable bimini: http://www.boat-links.com/Atkinco/Sail/Surprise.html

 

The Dipper looks nice and sturdy, but is too short of course. But lengthening is a new design. It is not just adding a few inches, unfortunately.
The Atkins would not need much to change, but a modern building method is again a new design either.

Maybe just look further! I would do so too, but I´m a bit short in time, have just today adopted a new project.

Regards
Richard

 

Torque BS

Since I am a spoil sport I will start by giving a physic lecture. For an engine with an ideal gearbox, the only important parameter is maximum power. Torque itself is not important, but since power is a function of torque (torque / second * constant), they are tied together. This torque ******** comes from the world of autos, which is operated under different conditions. If you select a gear which lets the engine reach the maximum power (often close to max rpm), then two engines with the same maximum power will render the same result. "Low torque" can always be compensated for with an ideal gearbox. In practice, no gearboxes are ideal, so torque is somewhat important, especially for trucks, and even for boats. But in this case, a one speed reduction gear would probably solve it.

 

You all forgot to mention a gen set has a constant speed govenor and a marine engine or a vehicle engine has a variable speed govenor
Its not just a spring and a lever on the side of the engine

 

Search this site for Rob White and Rescue Minor , it may be the boat you want.

For most folks there is no need for a brand spanking new engine, the 2 or 3 cyl Yanmars or Kubotas can be had running used from truck reefer sets.

A couple of hundred bucks will get a running take out , and as many are specific built as truck reefer (refrigeration)units , they will have HUGE !! oil pans to allow 2 weeks of operation , nonstop , with no service.

FF

 

********,

you are right, complete bs............

One needs torque to turn a big wheel, or more torque.

 

FF --
Where does one look for one of these used "refer" units?

Here is yet another set of lines, up for consideration. I've already ordered the print: http://www.cbmmstore.org/yaorstisskpl.html

John Gardner also has a set of lines and offsets for a Staten Island Skiff in his book, Classic Small Craft You Can Build. He has modified the lines pretty significantly (increased the beam by one foot, raised the sheer amidships by several inches, modified the stern with +8" of drag).

While John has offered relatively few power boat plans, at least 3 were spec'd for very small diesels, on the order of 7 - 10 hp: his 22'5" x 6'8" working garvey, his 18' x 5'8" Seabright skiff and the 26' x 6' Hammond power dory.

I have no experience with low-powered displacement hulls, except for having been in a few 20+' sailboats while under power; my assumptions are based on Mr. Gardner's and other writings.

Along with possibly being a good match for this engine, the Yankee or Staten Island skiff may fit my previously stated notion:

 

I don't know anything about boats or the engine the OP asked about, but anyway...

I used to have a push lawnmower that came with one of the constant-speed governors. The throttle on the carb was hooked to a wire linkage, to a moving lever that came out of the crankcase, up near the cylinder head. I decided I wanted to use that mower for thatching, and doing that requires a very low engine speed, or else it just shreds the grass.

I went to the local hardware store/mower repair place and asked them about converting the mower to a manual throttle, and they said that the mowers now that are single-speed usually have a single-speed carburetor. Even if you connect the carb butterfly to a manual control cable, you will NOT get full-range of engine control by manipulating the butterfly. You will usually only get maybe 20% below the set RPM, to maybe 20% above the set RPM, and that's it.

To get full-range speed control, they said I would need to track down a full-range carburetor that would fit the engine (or make one fit that was about the same size) and put that on in place of the single-speed.

Well,,,, the mower wasn't worth that much cost or effort, but when I got home I tried disconnecting the throttle link and moving the butterfly with a pair of needlenose pliers anyway. And just like the guy said,,,, the carburetor would not control the engine over it's full range (from barely-running to obviously-too-fast). The carb's speed control range was only about what he said it would be.

--------

I have no idea what kind of carb that Yanmar comes with, but you may want to talk to somebody who has already done this modification before you order one. Controlling it usefully may not be as easy as just disconnecting the governor and adding a manual control cable to the fuel/intake system.
~

 

Interesting story DougCim. How would you start an engine that only runs at 3000 rpm? By pulling that fast?

The Yanmar is a diesel, so no carb, no butterfly valve....

 

You can pull-start it, but even with the butterfly held all the way "closed", it immediately climbs to a minimum speed that's 80% or so of the intended RPM.

Yea I know, I didn't say it did.

Before ordering, you still might want to ask at any local repair shop that works on diesel engines these sizes if there is a similar issue with converting them to a full-range manual throttle.
Previous to my own lawnmower incident, I'd have not thought a single-speed carburetor even existed....
~

 

Tourqe is power divided by gearing

Torque at propeller shaft is power / gearing * constant. If you want more torque (at the propeller shaft), select a different gear ratio. It is POWER which produces torque at the propeller shaft. You are right that you need tourque, but the engine does NOT need high tourque. An F1 car has high power, low torque and hence many gears. The only advantage of an engine having high tourque is that you need fewer gear ratios. In this case you should only need one, but you may be right that a two speed gearbox may be necessary, if the engine has low torque. In that case, it may be smarter to select the engine you mentioned.

OK?

 

Right now with this economy the world is awash with good boats for sale at reasonable prices. I came across this Chris Craft in southern New Jersey with twin diesel engines at a reasonable price. Take your time look and see what is available in your area for sale. You may be pleasantly surprised. http://southjersey.craigslist.org/boa/1889765308.html