A little advice regarding max hp/weight.

[TimSharpe]

Hi hope this is in the correct section. I've recently purchased a 2.3 waveline slatted floor dinghy. Brand new which states max engine weigh 20kg and max hp 3. I was using a British seagull engine which died at the weekend so looking for a new outboard. I've noticed the 2.6 waveline max hp is 5 and max weight is 32kg. I was hoping to put maybe a 4 or 5 hp motor on my 2.3 but unsure how forgiving those figures are likely to be.

Any tips or pointer appreciated thanks

 

[lw395]

You may find the 5HP just folds the dinghy in half and doesn't go any faster.
I really don't regret going down from 4HP to 2 HP with a similar size flubber.

 

[James_Calvert]

You're thinking of creating a mismatch.

Too much weight and power at the back of a small dinghy can be inherently dangerous especially in the wrong hands.

Why exceed the manufacturer's limits?

Maybe a bigger dinghy would suit better anyway.

 

[Baggywrinkle]

Difficult to tell, may just make alot of noise, use more fuel but not go much faster, it may bury the nose under waves when you open her up while fully loaded, and if you get it planing, the directional stability won't be great due to the flat bottom.

My 6hp Mercury 4-stroke weighs 27kg - it works well on a 2.7m airdeck but still ships water over the front with people sitting on the bow when I try to go too fast. 2 up it planes nicely and is directionally stable.

The weight and HP limits are due to the relatively short length and reduced weight - which translates into a lessened ability to keep the nose down when you open up the throttle while sitting at the back with a heavy engine .... IMHO, to get the most out of a 5 or 6 hp you really need a slightly longer dinghy with an air-deck or V hull so it will plane 2 up with a bit of directional stability.

As a kid I used to get our avon redcrest planing with a seagull by crouching behind the bow and extending the tiller with a broom handle, but I only weighed 40kg and it was great fun :encouragement:

Why not see if you can try a 5hp on it? ... and there are lots of videos on YouTube where people put big outboards on small inflatables with entertaining results.

 

[TimSharpe]

Thanks for the replies guys. I'm really just looking for something that isn't going to feel like a snails pace the way the old 2hp seagull did. I understand I'm going to have limited directional stability. I'd like to if possible be able to get it planing. I also dont want to take any unnecessary risks with regard to the specs hence why I've posted here.

I'm thinking a mercury 3.5 four stroke may do the job?

 

[Graham376]

You're thinking of creating a mismatch.

Too much weight and power at the back of a small dinghy can be inherently dangerous especially in the wrong hands.

Why exceed the manufacturer's limits?

Maybe a bigger dinghy would suit better anyway.

My 7 year old Waveline 2.9 is plated for max 10 hp but, if I buy a new one, exactly the same model, it's now plated for max 6 hp. I'm told this is because 4 strokes are much heavier, not because of power. I have a 9.8 2 stroke (same weight as a 6 hp 4 stroke) which would be fine on a new dinghy but, in the case of an accident could be in a sticky situation for exceeding manufacturer's limits, it's the kind of thing police here look at.

 

[lw395]

Thanks for the replies guys. I'm really just looking for something that isn't going to feel like a snails pace the way the old 2hp seagull did. I understand I'm going to have limited directional stability. I'd like to if possible be able to get it planing. I also dont want to take any unnecessary risks with regard to the specs hence why I've posted here.

I'm thinking a mercury 3.5 four stroke may do the job?

Unless you regularly have significant distances to go in your tender, the time saved by going at planing speeds where you can does not always add up to very much. I found the smaller lighter 2HP engine saved time because it's so light to ship and unship, easy to carry up the beach instead of going to the quay etc.
Anything much under 8HP is often hard to pushed to plane except in really flat water two-up.
Mostly we are going across harbours, across the waves, so half hearted attempts at going fast just result in getting wetter for not much benefit. If you're going down that route IMHO there's not much benefit until you get to 15HP and a proper v-bottom boat on davits on your 45ft boat.
The 2HP is also much easier for SWMBO to start which is a big bonus.
The 4HP was better driving a rigid tender upwind against the chop and would surf coming back.

 

[TimSharpe]

Unless you regularly have significant distances to go in your tender, the time saved by going at planing speeds where you can does not always add up to very much. I found the smaller lighter 2HP engine saved time because it's so light to ship and unship, easy to carry up the beach instead of going to the quay etc.
Anything much under 8HP is often hard to pushed to plane except in really flat water two-up.
Mostly we are going across harbours, across the waves, so half hearted attempts at going fast just result in getting wetter for not much benefit. If you're going down that route IMHO there's not much benefit until you get to 15HP and a proper v-bottom boat on davits on your 45ft boat.
The 2HP is also much easier for SWMBO to start which is a big bonus.
The 4HP was better driving a rigid tender upwind against the chop and would surf coming back.

I'd be using it mostly for exploring loch lommond and the islands on the loch. Also some tidals rivers. So not a huge amount of speed required but enough to get across the loch in reasonable time. Also maybe a bit of pottering about around the coasts and bays of Scotland.