Low power saildrive

[frank pedersen]

Surely one of the best things about the WBF is the opportunity for reality-testing of wacky ideas. So here is my proposal: I am interested in an affordable, low-power ( say 4.5 h.p.) saildrive unit for a light-displacement sail boat. The Saildrive 330 (www.saildrive.us/index.html) is 15 h.p., weighs 110 lbs. plus battery and gas tank, and cost $6,800. My question: Would it be possible to modify a 4.5 h.p. Yamaha 4-stroke OB to convert it to a saildrive? I don't want merely to put an OB in a well in the cockpit. Some saildrives I have seen on boats look like the lower end of an OB with the fins ground off. I have thought if I can get a "dead" saildrive and a "dead" Yamaha OB, I could see if I can make the mechanical parts to fit together - the mounting brackets, grinding off the fins, etc. If it seemed plausible, then I might go ahead and risk the cost of a new motor. What do you think?

[willmarsh3]

I think I would stay with the outboard well for a couple of reasons. I've seen where rubber sheet is placed in the bottom of the outboard well with a slit to plunge the bottom end through. You get a smooth surface under water like you'd get with a saildrive. But you don't have to modify the motor and it is easier to remove for servicing. Or perhaps you can fit doors on the underside opening of the outboard well to fit the contours of the outboard. Easy to go back to the rubber sheet if it doesn't work.

I like to tinker but I'm quite hesitant to modify a brand new outboard without carefully thinking it through so it's great that you are asking.

My experience is limited to outboards and inboards but not saildrives. Given how an inboard engine vibrates, a sail drive would most likely need to be carefully engineered to minimize vibration where it passes through the hull.

[paladin]

I thought about the same thing for a long time...to the point of actually researching and working out the mechanicals including soft mounts and a soft CV coupling......but....the drag is still higher than with other methods...and a bit more complicated.

[BrianM]

Don't forget, outboard motors were not built to take pressure on their water intakes, nor gearbox seals beyond the typical depth of submersion an outboard sees. Saildrives must be more rugged since they are so far down.

[Brian Palmer]

Does anybody make feathering props for outboards? It seems the saildrives are fitted with feathering props to reduce drag under sail. That would also reduce the drag of an outboard in a small well and reduced the need to pull it up under sail.

Brian

[py]

Expanding on the rubber flap idea, could you perhaps have a well, but actually seal with some rubber sheet between the hull and the outboard leg? So that you have no water in the well, a nice smooth bottom. If its held on with say a hose clamp, easy enough to remove the O/B for servicing etc. You'd want to shut off the little cooling water spurt, which I think is only there to tell you that the colling water is in fact circulating.

[andrewe]

I am actually working on one (slowly, as it is not needed till later this year--or next)
One problem for your system is that you cannot immerse the engine lower than it would be normally as the exhaust would flood up to the cylinder. Seperating out the exaust to a trap and hull fitting sounds a lot of work.
Welding a flange on the leg to attach the rubber diaphram could be feasable, but I would want a well in case of failure. Solid bolting to the hull would be very noisy.
British Seagull made one for a short time, aimed at small fishing boats. Popularity was not helped by a defective con-rod design that failed if over revved a bit. A collecters item now.
The Volvo Penta 7.5hp. Sail-Drive was based on a Honda 4-cycle outboard.
Andrew

Just re read your post, if combining a 'dead' sail drive, why stick to an O/B power head? Plenty of other engines out there. Have a look at Donald Branscome's Honda instalation in his 19ft sailboat. Same applies if using an o/b leg (as I am) The impellor pump could supply cooling water for a seperate exhaust. A

[floatingkiwi]

What are the differences between an OB and a saildrive?

[rbgarr]

Expanding on the rubber flap idea, could you perhaps have a well, but actually seal with some rubber sheet between the hull and the outboard leg? So that you have no water in the well, a nice smooth bottom. If its held on with say a hose clamp, easy enough to remove the O/B for servicing etc. You'd want to shut off the little cooling water spurt, which I think is only there to tell you that the colling water is in fact circulating.

My father did this on an Amphibicon in the 1960s with two overlapping pieces of inner tube. A separate tube and through-hull outlet for the exhaust and cooling water was needed and installed as well. The motor was an Evinrude 18, a pretty big, smoky piece of two stroke iron. It worked alright but not great.

I'm pretty sure Frank doesn't want and may not even have the room he'd want to give up for a well on his boat.
http://i39.tinypic.com/25iz0jk.jpg

If you haven't seen the Andrew Sims' Wavelengh Studios photos of the Eggemoggin Reach Regattas, they are worth seeing: www.wavelengthstudios.com

[D Happ]

I've been thinking about the same thing since I started messing with this and installing it.
This is a 1977 OMC Saildrive. 15hp. The power head is Johnson/Evanrude 35 hp de-tuned to 15 hp, or so they say.
http://users.gotsky.com/dhapp/S6301247.JPG


http://users.gotsky.com/dhapp/S6301249.JPG

I've realized there are a few problems associated with this beside the water tightness of the hull fitting.
The exhaust on this engine is a water cooled jacket and I would think it would take a lot of work to adapt an outboard with a water cooled exhaust. Not sure I would want a screaming hot exhaust in my boat. A water jacketed exhaust might consist on making a new exhaust manifold.
Second would be the carburetor. there are special requirements for carburetor engines inside the confines of a boat. Not just flame arrestors but this air box has a well for storing fuel should some burp out of the carburetor, which is then drawn back into the carburetor. The instruction manual is very specific about having this in place on this engine.
As far as water pressure is concerned, there is 1 psi for every 2.3' of water, so the increase might only be 2 psi.
This engine has a valve in the cooling water system that can be closed and the power head removed while the boat is in the water. Pretty specifically designed system.
Please bear in mind I don’t know anything about outboard engines, only this saildrive.
I hear some talk of an electric saildrive that uses the prop to re-charge the batteries once underway. That might be easier to do.
If I had money, I’d buy a Buhk Diesel saildrive. http://www.bukh.dk/produkter/uk/products_DV10Lsme.htm

[Thad Van Gilder]

I had a friend who bought a 2.5 hp or thereabouts diesel outboard from india for a grand. he planned on doing the exact same thing with it.

after a year or two of fiddling, he sold the outboard and gave up.

-Thad

[frank pedersen]

Thanks guys. You have given me a lot of food for thought. And Dave, thanks especially for the picture ( I know you told me how to do it, but I am somewhat retarded in that area.) Among my thoughts are the following: (1) It seems too difficult for me to try to construct a home-brew saildrive from an outboard. (2) Considering all the beautiful, good-sized boats that manage largely without power, e.g. Int. One Design, 6-Meter, Dragon, Rozinante, 210, Shields, Alerion, etc. (Have I forgotten anyone?), I can do that as well. (3) For the few times I have needed power, my 2 1/2 h.p. Honda OB with a transom-mounted bracket has done the job adequately even though the aggravation factor is significant. There is a picture on pg. 40 of the first edition of WB's Small Boats that shows the bracket I have on the transom. (4) I am going to change the placement of the tangs the backstay attaches to, moving them further outboard. That should make it easier to slip the OB and its mount into the bracket without either the OB, me (or crew), or both falling overboard. Thanks again. Frank

[TMny]

A small 'gin pole' [or related contraption] , mounted/stabilized by a fitting(s) on the deck/boom/backstay might allow modifying the install/stowing procedure of the existing outboard in a way that makes it more fun than , say , setting a spinnaker (or suffocating inverted in a deep bilge while attempting calibration of a rarely functional instrument), etc. Modifying existing systems (with information based on in situ user-experience) is frequently simpler , and yields more definable improvement than an entirely new implementation , particularly when there are any limits on budget. Rare is a stock install that could not profit by 'field improvement'.

Consultation with an orthopaedic surgeon to add 'hands'&'eyes' to the 'feet' would also improve the stability of the normal (not to mention age-distended) human physique during the related procedures ....

[rbgarr]

Logorrhea?

[floatingkiwi]

A small 'gin pole' [or related contraption] , mounted/stabilized by a fitting(s) on the deck/boom/backstay might allow modifying the install/stowing procedure of the existing outboard in a way that makes it more fun than , say , setting a spinnaker (or suffocating inverted in a deep bilge while attempting calibration of a rarely functional instrument), etc. Modifying existing systems (with information based on in situ user-experience) is frequently simpler , and yields more definable improvement than an entirely new implementation , particularly when there are any limits on budget. Rare is a stock install that could not profit by 'field improvement'.

Consultation with an orthopaedic surgeon to add 'hands'&'eyes' to the 'feet' would also improve the stability of the normal (not to mention age-distended) human physique during the related procedures ....

What the.....?

[andrewe]

I think TMny might be refereing to ' re-inventing the wheel' or mouse-traps or similar. Or possibly exploiting a non-existant market.

Some of us just enjoy tinkering;)
Andrew

[frank pedersen]

Not to belabor this excessively, buy TMny's mention of an orthopaedic (or orthopedic) surgeon may not be entirely off the wall. My daughter, who is a physical therapist, is a terrific crew with me in my Wayfarer. It is an aside point that some years ago she was run over by a car and had an above knee amputation. When we raced she put her prosthesis under the foredeck (it could serve as an extra whisker pole), but now she has a "C-leg" - a computerized prosthesis that is too expensive to risk salt-water damage (like B.D. in Doonsbury.) She manages the spinnaker too, and she says there is some advantage in hitting only one shin when we come about. But I digress. To get back to TMny, I'm going to ask her to observe how we put the outboard on the transom. Through her work as a physical therapist, she might have some advice on how to brace one's body, get support when performing an awkward physical maneuver, or exercises to strengthen the muscle groups involved.

[rbgarr]

The stand-alone electric Torqeedo weighs less than 30 lbs and folds. I'm waiting to see if the product has 'legs'. It might be the kind of motor we could all use on different boats in the 'family fleet'.