size of outboard for boat
Discussion
was gifted a 15' fibre glass clinker boat weighs 600kg , has a 20" transom , was wondering what's the best outboard to fit , and what would be the maximum weight the transom could take
looking at Tohatsu as they are very fuel efficient and lowest weight in class the 30hp is 58 kg the 20 hp / 15hp both weigh 43 kg the 9.9 weighs 38kg 8hp is 37kg
this is a similar boat using a 20hp , would be using in poole harbour
looking at Tohatsu as they are very fuel efficient and lowest weight in class the 30hp is 58 kg the 20 hp / 15hp both weigh 43 kg the 9.9 weighs 38kg 8hp is 37kg
this is a similar boat using a 20hp , would be using in poole harbour
Edited by Purosangue on Thursday 27th February 16:48
sherman said:
Call that an outboard?This is an outboard:
600hp 7.6l V12
https://www.mercurymarine.com/us/en/engines/outboa...
(Sorry OP!)
Purosangue said:
was gifted a 15' fibre glass clinker boat weighs 600kg , has a 20" transom , was wondering what's the best outboard to fit , and what would be the maximum weight the transom could take
What is the make? That would be the first stop if there is no makers plate, anything post-RCD will have info like that on the plate. Some pics would help too. Depends on the hull shape.
A 15ft speed boat will take 70HP. It will plane at maybe 40 knots.
A 15ft displacement hull won't benefit from much more than say 10HP, it will only do about 6 knots and any more power just creates a lot of wash and uses a lot of fuel.
Clinker hulls tend to be displacement. But there are exceptions.
Also, where are you going to use it? A river or canal will a 5mph speed limit, you only need a small motor.
IF it's displacement mode, you want a 'saildrive' type outboard, with a big fine pitch prop.
A lot of 15ft boats would be OK with 4HP rather than 10, but the OP's boat is on the heavy side.
Fourstroke is quieter and more economical, 2 stroke is lighter.
Electric is an option, but not cheap.
A 15ft speed boat will take 70HP. It will plane at maybe 40 knots.
A 15ft displacement hull won't benefit from much more than say 10HP, it will only do about 6 knots and any more power just creates a lot of wash and uses a lot of fuel.
Clinker hulls tend to be displacement. But there are exceptions.
Also, where are you going to use it? A river or canal will a 5mph speed limit, you only need a small motor.
IF it's displacement mode, you want a 'saildrive' type outboard, with a big fine pitch prop.
A lot of 15ft boats would be OK with 4HP rather than 10, but the OP's boat is on the heavy side.
Fourstroke is quieter and more economical, 2 stroke is lighter.
Electric is an option, but not cheap.
hidetheelephants said:
Purosangue said:
was gifted a 15' fibre glass clinker boat weighs 600kg , has a 20" transom , was wondering what's the best outboard to fit , and what would be the maximum weight the transom could take
What is the make? That would be the first stop if there is no makers plate, anything post-RCD will have info like that on the plate. Some pics would help too. 
boat came from Christchurch , as a freebie one of those must be collected today !! i...............hence the heath Robinson 6' trailer conversion process of re gelling it and re furbishing the wood , structurally she's sound ..........also have a proper boat trailer to launch .
no name plate , ideally take out into pool harbour for fishing
It's a nice big rowing dinghy, for sheltered water like Poole Harbour anything more than 5hp is a waste of money and fuel; open water you might go up to 10hp but would have to watch for the transom flexing under power and also observe the fore-and-aft trim carefully as it doesn't have the right hull shape to carry a large motor and there isn't an outboard well to catch waves at the stern.
Edited by hidetheelephants on Thursday 27th February 22:21
We have a 16 foot fibreglass hulled gaff rigged boat similar to yours, but with a cabin. It was bought from an experienced chap in Poole and it was / is fitted with a 5hp outboard.
He explained to us that the 5hp was a little big and a bit of an overkill, but that Poole harbour had a very strong tidal current and without that size engine, the boat wouldn't have been able to get through the current.
I hope this is of help and your boat could look quite good!
He explained to us that the 5hp was a little big and a bit of an overkill, but that Poole harbour had a very strong tidal current and without that size engine, the boat wouldn't have been able to get through the current.
I hope this is of help and your boat could look quite good!
mkjess123 said:
We have a 16 foot fibreglass hulled gaff rigged boat similar to yours, but with a cabin. It was bought from an experienced chap in Poole and it was / is fitted with a 5hp outboard.
He explained to us that the 5hp was a little big and a bit of an overkill, but that Poole harbour had a very strong tidal current and without that size engine, the boat wouldn't have been able to get through the current.
I hope this is of help and your boat could look quite good!
Hi thanks for all the replies , I have all the wood working tools and chap next door has boats and loads of gel coat , this is the type of finish Im looking to get her for summer . He explained to us that the 5hp was a little big and a bit of an overkill, but that Poole harbour had a very strong tidal current and without that size engine, the boat wouldn't have been able to get through the current.
I hope this is of help and your boat could look quite good!
yes will get some oars , was looking at a brand new Tohatsu outboard funny thing I have a 2.5 Hp suzuki in the garage but its a short shaft . The chap I got her from had her down at Christchurch Marina He had a deadline to get rid hence she appeared free on Gumtree , The caveat you need to bring a trailer , a lot of people said they would fit on the roof rack .... without realising the weight . It took four of us to get her on to my extended trailer then a very carefull drive back home going the back roads
cheers
A 8-9.9hp would be fine on that. Mainly so that you wouldn't have to run at full chat all the time to get it to go anywhere. It would also give you some shove against tide. Still quite lightweight so unlikely to do any damage to the transom. I would suggest asking the chap who is doing the restoration for you.
jonathan_roberts said:
A 8-9.9hp would be fine on that. Mainly so that you wouldn't have to run at full chat all the time to get it to go anywhere. It would also give you some shove against tide. Still quite lightweight so unlikely to do any damage to the transom. I would suggest asking the chap who is doing the restoration for you.
thanks , Tohatsu do an 8hp or 9.9 hp , the transom looks in very good condition , im going to strengthen it when i refurbish the wood im doing the restoration myself as a spring project.
cheers
Purosangue said:
jonathan_roberts said:
A 8-9.9hp would be fine on that. Mainly so that you wouldn't have to run at full chat all the time to get it to go anywhere. It would also give you some shove against tide. Still quite lightweight so unlikely to do any damage to the transom. I would suggest asking the chap who is doing the restoration for you.
thanks , Tohatsu do an 8hp or 9.9 hp , the transom looks in very good condition , im going to strengthen it when i refurbish the wood im doing the restoration myself as a spring project.
cheers
hidetheelephants said:
OutInTheShed said:
Bargain outboards are often not 100% reliable, so maybe try to acquire or borrow some oars and rowlocks too!
Very much! If nothing else a nice dinghy like that will row really well.People have mentioned fighting the tide, boats' speed through the water is what matters, you can't just add extra power for the tide.
The thing that really absorbs power is chop or waves. Flat water is easy, a heavy boat loses a lot of energy every time it smacks into a wave.
It's also important to have the right propellor, to match the engine to the boat. A couple of HP will push my yacht along at 4.5knots in flat water, but my 2HP outboard has a prop that's better for pushing a small inflatable dinghy at 8 knots or more. A decent amount of thrust also makes manoeuvring a whole lot easier... A bit of spare power makes the finer points of prop choice less critical.
As with cars, people with electric outboards bang on about the low down torque and there's some truth in that, but range anxiety is whole different thing afloat.
I spent a lot of time investigating best power/weight for a small outboard for my 26ft race sailboat. the answer was a long shift tohatsu 9.8 2 stroke at 27kgs. It was light enough to be lifted off the transom in bumpy conditions for stowage when racing and at half revs easily dealt with spring tides getting in out of hamble to racecourse. I think it or similar would be ideal for your application. My engine is sitting unused in a workshop at hamble with external tank etc - new raceboat is very lightweight carbon skiff and much smaller 3.5 outboard at 17kgs is fine so my 9.8 is no longer used if interested in engine pm me. they are generally available - I wholeheartedly recommend them - much lighter than boat anchor 4 stroke
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