USER888
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What HP to get for 4-stroke outboard for 25 foot, 2.5-3ton yacht?
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VicS
Well-Known Member
I'd think probably about 9.9.
Although you cannot drive the boat any faster than its waterline length allows it makes sense to be able do that against a strong wind and a chop.
Advisable to choose a "sail" version as that should come with a prop suitable for pushing a displacement hull, and probably a long shaft and an electrical output for battery charging.
Although you cannot drive the boat any faster than its waterline length allows it makes sense to be able do that against a strong wind and a chop.
Advisable to choose a "sail" version as that should come with a prop suitable for pushing a displacement hull, and probably a long shaft and an electrical output for battery charging.
ReefMagnet
Active Member
I had a similar size and weight boat for a few years. It had a Yamaha 9.9 hp xl shaft hi thrust outboard that was absolutely perfect and could push it unstressed through just about any conditions.
Edit: If you just want to move around in still air I think the rule of thumb is 2 hp per ton so a 5 hp would do the job. Would still need to be an xl shaft though I would suggest.
Edit: If you just want to move around in still air I think the rule of thumb is 2 hp per ton so a 5 hp would do the job. Would still need to be an xl shaft though I would suggest.
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onesea
Well-Known Member
OK Shifting round a Trident 24 I used 2 outboards...
First was 3.5hp 2 stroke tomhatsu - Would push her at 4 knots with clean bottom could maintain steerage in flat water against a F6. Any wind and motor sailing had her up to hull speed, she would motor sail to windward with main and outboard quite well.
Second was 6hp Mariner 4 stroke, which was adequate it easily reached hull speed in flat weather and clean bottom. Over F6 in a chop it struggled again motor sailing it was fine.
Would I of wanted bigger? No because I had to lift engine quite frequently and once over 6hp they become 2 cylinder and much heavier..
If not for this then yes a 9 or probably a 15 (they weigh the same) would be a good idea. Why a 15? modern 4 strokes do not like being run flat out, I guess that you would use less fuel and have happier engine. Also you can get electric start if that tickles your fancy.
On the 6hp I when ordered I just requested a high thrust prop. SO pick your shaft length to suit your engine, although IMHO a deep prop pushes better than one near the surface...
I did not get charging as I could not be bothered with the connections and for the minimal electric used I charged in marinas and on Solar.
First was 3.5hp 2 stroke tomhatsu - Would push her at 4 knots with clean bottom could maintain steerage in flat water against a F6. Any wind and motor sailing had her up to hull speed, she would motor sail to windward with main and outboard quite well.
Second was 6hp Mariner 4 stroke, which was adequate it easily reached hull speed in flat weather and clean bottom. Over F6 in a chop it struggled again motor sailing it was fine.
Would I of wanted bigger? No because I had to lift engine quite frequently and once over 6hp they become 2 cylinder and much heavier..
If not for this then yes a 9 or probably a 15 (they weigh the same) would be a good idea. Why a 15? modern 4 strokes do not like being run flat out, I guess that you would use less fuel and have happier engine. Also you can get electric start if that tickles your fancy.
On the 6hp I when ordered I just requested a high thrust prop. SO pick your shaft length to suit your engine, although IMHO a deep prop pushes better than one near the surface...
I did not get charging as I could not be bothered with the connections and for the minimal electric used I charged in marinas and on Solar.
William_H
Well-Known Member
Outboard size
Much depends as said on whether you intend to lift the motor off or if it will be a semi permanent installation.
Weight might become the critical factor. Just a few horsepower are fine for no wind motoring but if you find you want to motor into a wind and wave then you need more horsepower.
I find that for any large amount of motoring a single cylinder motor is very noisy compared to twin cylinder. So a lot sweeter but a lot heavier. It is all a compromise. My 6HP is more than adequate for 21ft. If I bought another motor it would be a tiny single perhaps only 2 HPbut light weight. good luck olewill
Much depends as said on whether you intend to lift the motor off or if it will be a semi permanent installation.
Weight might become the critical factor. Just a few horsepower are fine for no wind motoring but if you find you want to motor into a wind and wave then you need more horsepower.
I find that for any large amount of motoring a single cylinder motor is very noisy compared to twin cylinder. So a lot sweeter but a lot heavier. It is all a compromise. My 6HP is more than adequate for 21ft. If I bought another motor it would be a tiny single perhaps only 2 HPbut light weight. good luck olewill
AngusMcDoon
Well-Known Member
My twin cylinder Yamaha 9.9 XL shaft electric start has been off only once in 12 years. It was so heavy to lift I gave up and used a crane.
My engine is a lot quieter than Dylan's single cylinder Tohatsu. I have sailed on a boat with one installed, so can compare.
Zagato
Well-Known Member
I have a Yamaha 6HP twin cylinder, 4 stroke, 38KG (nice and quiet 
) on a 1 tonne 22' boat. If you are against a tide or trying to get through a marina lock on free flow I wouldn't want any less power...
I had a 9HP Yanmar inboard on my 2.5 tonne Folksong 26 and wouldn't have wanted any less!
I would go for the 9HP+ power that folk suggest if lifting is not an issue, you never know when you might need the power to get you out of trouble, better to get the right tool for the job
) on a 1 tonne 22' boat. If you are against a tide or trying to get through a marina lock on free flow I wouldn't want any less power... I had a 9HP Yanmar inboard on my 2.5 tonne Folksong 26 and wouldn't have wanted any less!
I would go for the 9HP+ power that folk suggest if lifting is not an issue, you never know when you might need the power to get you out of trouble, better to get the right tool for the job
Lakesailor
Well-Known Member
I'm not sure if you mean you've sailed on a similar boat to Dylan's. Consensus was that the inboard well and the shape of the transom inner moulding makes his motor seem noisy. I've had a Mariner 4hp and Tohatsu 5hp (both 4 strokes and both the same basic motor, as well as the 6hp including the Mercury versions)) and they are quiet engines.
Forumites have been on the boat and have remarked on the silent progress.
AS to the point someone made about the 9hp and 15hp being the same motor. The extra power is mainly produced at higher revs, so whilst it is available if required (?) the 9hp would be more than adequate, less thirsty and less money.
lw395
Well-Known Member
It depends what value you place on being able to go fast under motor, vs cost and effect on sailing performance.
40kg or whatever hanging on the transom will degrade the sailing performance in waves.
On 21ft tonne-and-a-bit keel boats we find 3.3hp Yamaha Maltas best. But 2hp will do the job if that's what you have. It's got a lot to do with having the right prop.
3.3Hp will allow one boat to tow another into Portsmouth Harbour against the ebb. Just!
If you want to bash into waves, you will need a lot more power though.
40kg or whatever hanging on the transom will degrade the sailing performance in waves.
On 21ft tonne-and-a-bit keel boats we find 3.3hp Yamaha Maltas best. But 2hp will do the job if that's what you have. It's got a lot to do with having the right prop.
3.3Hp will allow one boat to tow another into Portsmouth Harbour against the ebb. Just!
If you want to bash into waves, you will need a lot more power though.
CAPTAIN FANTASTIC
Well-Known Member
I have a Tohatsu 4 stroke 6hp long shaft; I have used it over the years on an inflatable tender (2.9m) and also to power my Macwester Wight which is 5 tonnes and carries a lot of drag under the water (twin keel), when the inboard diesel was out of action for a bit.
The Tohatsu drove the Yacht nicely and I was impressed with the power; the good thing with the 6hp is that you can lift it easily, any bigger and you should be looking for davits. The reliability of the tohatsu is great.
The Tohatsu drove the Yacht nicely and I was impressed with the power; the good thing with the 6hp is that you can lift it easily, any bigger and you should be looking for davits. The reliability of the tohatsu is great.
C
catalac08
Guest
A couple of posters have mentioned the Yamaha or Tohatsu 9.9 extra/ultra long shaft. This is obtainable as a "saildrive version" which has a bigger diameter prop than a standard 9.9 propellor because the gear ratio is higher than a standard 9.9 which is much better for driving a displacement hull. Strangely neither of these makers do a saildrive (bigger prop/higher gear ratio) version in the bigger engine sizes.
There are many catamarans with more windage and weight than your boat that work very happily on one of these 9.9 saildrive outboards. Unfortunately they do not do a power tilt in the 9.9 engine size.
There are many catamarans with more windage and weight than your boat that work very happily on one of these 9.9 saildrive outboards. Unfortunately they do not do a power tilt in the 9.9 engine size.
alahol2
Well-Known Member
Had the Yamaha 9.9hp High Thrust on a 32ft Cat for 13 years. Superb engine in all respects. Never felt the need for more power, would push a battleship.