Long Shaft outboard too long for a Dory?

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BlueSkyNick

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I am planning to buy an old Orkney or Dell Quay Dory for use as a tender - probably 11ft. In order to shift 4 adults with gear against the tide and wind, I want a 15hp or 20hp outboard. These all seem to be long shaft - no short shafts available on boatsandboards or ebay.

Assuming depth of water is not an issue, will it matter having a long shaft engine on a shallow draft boat? I always thought this was a bad thing as the bow comes too high out of the water.
 
Keeps the prop in the water .. Watch out for shallows .. Someone told me that the prop should be just under the water but how do you explain an inboard thats about 300mm under water .. Beg or borrow one and give it a try .. Happy Surfing /forums/images/graemlins/laugh.gif
 
Conventional wisdom generally says that you want the big horizontal plate (just above the propeller) on the outboard engine to be approximately in line with the bottom of the hull.

If it is a bit deeper, then there will be a bit more drag, and draft.
You could perhaps raise the transom locally in way of the outboard engine so that it is mounted higher up if this is an issue (?).

Dell Quay Dories, Boston Whalers et al generally tend to trim fairly level when on the plane - if there is an issue with the bow coming up too much then moving the crew weight forward a bit should solve the problem.

The Yamaha dealer here likes to install his outboard engines as high as possible, while keeping with the main constraint mentioned above. He has a point - some big outboards on deep vee planing boats here are so deeply immersed that the lifting devices for tilting the engines are underwater, which cannot be very good for them.
 
Surprised you cannot get a std shaft model.

I have an old Evinrude catalogue which lists both standard (381mm ) and long (508mm) versions of engines up to 75hp.
(The dimensions I quote for "shaft length" are the heights of the transom top above the water line.)
The water depth and and grounding risks may not be important factors but the increased back pressure on the exhaust system is usually given as the reason for not using a long shaft model where a standard shaft one should be used as it may making starting more difficult and adversely affect fuel consumption and performance perhaps. The effect on trim is also a factor i guess especially using a fairly powerful (and heavy) engine on a small boat. It might help get it up planning though other wise keep something heavy in the bow.

Must admit though that I use a long shaft engine rather than a standard shaft without noticing that it is difficult to start.

Keep looking but if you see a good one that's a longshaft at a decent price buy it.
 
Isnt there a twisting effect on the tramson from the outboard?
Inst the thrust trying to force the propeller forward? If it was lower wouldnt it have more of an effect?

If it was not the maximum hp for the boat i dont suppose it would matter??

Any thoughts?
Rob
 
the only problem is starting it, the exhust it lower in the water and it need a little more power to overcome the back pressure, but with a small engine should not be a problem.
 
Hi Nick It wont be as much fun as getting a wet arse in the rib. /forums/images/graemlins/smile.gif

Just a thought,the RNLI sometimes sell off outboards. they use 15 horse ones on boarding boats in some places. Could be worth a chat with local coxswain or phone their head office.One thing for sure is it would have been well maintained.

On a big dinghy such as you are looking for I dont think it will matter ,on a small dinghy with the helm hard over a longshaft can cause a capsize due to the leverage effect.
 
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Surprised you cannot get a std shaft model.

[/ QUOTE ]
Vic , I am sure std shafts are available its just that the second hand market seems to be over 80% long shaft.

as i will be using it up and down a river as a tender, not a seagoing rough weather boat, I guess I will get away with either.
 
Graham, you can sit on the bow if it makes you feel better!

This thread has reminded me of when I was a teenager sailing with my Dad in Saundersfoot. We had a Leisure17, initially with a Seagull40 on the o/b bracket. It was a std shaft so whenever he or my lardy brother went forward, the prop would come out of the water.

So the old man went up market in the second year and traded the 40 for a Seagull Century. Not only did the prop stay in the water, we had more power and best of all it had a clutch! This meant we didnt have to kill the engine and judge the drift onto the mooring - in a harbour full of bow&stern moorings.

Oh happy days! /forums/images/graemlins/cool.gif
 
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