Outboard engine Size

FlyingGoose

FlyingGoose

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Afternoon fellow Sailors ,
I have had the unfortunate experience of having my 15 hp honda short shaft stolen of my Dinghy,
and was wondering as I need to buy a new engine what size would the members recommend for a 3.1 m fiberglass bottom Rib,
looking to take 2 adults 2 kids , and getting it onto plane , so we are not all sitting at the front jumping up and down, the smaller the better as 15hp was great but heavy and not suited anymore for moving and keeping on the transom of the new boat.
thanks again
 
My 6hp four stroke Tohatsu will go on a plane with two lightweight on a 2.9 v hull inflatable. I think the minimum in your case would be 10 hp (new engine, as an old 10hp engine will not develop its full power)
 
CAPTAIN FANTASTIC said:
My 6hp four stroke Tohatsu will go on a plane with two lightweight on a 2.9 v hull inflatable. I think the minimum in your case would be 10 hp (new engine, as an old 10hp engine will not develop its full power)
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ty yes I was thinking 10 hp was minimal but have never experienced other engines as this is still new to me ,
ty for your thoughts
 
FlyingGoose said:
Afternoon fellow Sailors ,
I have had the unfortunate experience of having my 15 hp honda short shaft stolen of my Dinghy,
and was wondering as I need to buy a new engine what size would the members recommend for a 3.1 m fiberglass bottom Rib,
looking to take 2 adults 2 kids , and getting it onto plane , so we are not all sitting at the front jumping up and down, the smaller the better as 15hp was great but heavy and not suited anymore for moving and keeping on the transom of the new boat.
thanks again
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What are the recommendations from the dinghy manufacturer ?

From an old Avon catalogue for a similar 3.1m RIB they suggest engines in the range 5 to a maximum of 10hp, with a capacity up to 420kg or 5 persons

Performance figures, with 2 persons on board, are: 11 mph with a 6 hp engine, 14mph with 8 hp and 20 mph with 10 hp.

Using an engine greater than the dinghy manufacturers recommendations could invalidate your insurance
 
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VicS said:
What are the recommendations from the dinghy manufacturer ?

From an old Avon catalogue for a similar 3.1m RIB they suggest engines in the range 5 to 10hp. (10 Hp being the max recommended size) with a capacity up to 420kg or 5 persons

Performance figures, with 2 persons on board, are: 11 mph with a 6 hp engine, 14mph with 8 hp and 20 mph with 10 hp.
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good point I will have a look its a walker bay SUPERTENDER 325 DELUXE, came with the boat, I just need it to move around and explore without the bottom end sitting in the water got 2 large mutleys to get to the beach as well for their morning and afternoon runs.
The boat will splash in April for our first trip on this boat so trying to get it all ready
 
FlyingGoose said:
good point I will have a look its a walker bay SUPERTENDER 325 DELUXE, came with the boat, I just need it to move around and explore without the bottom end sitting in the water got 2 large mutleys to get to the beach as well for their morning and afternoon runs.
The boat will splash in April for our first trip on this boat so trying to get it all ready
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Cums , look like 15 to 25 Hp ( 20 to 30 with a console ) ...
 
I chose the Tohatsu 18hp It is the same weight as the 15. It seems to have a little more grunt than the Yam 15 but who knows.

The only down side that I know of and this only matters if you have a sensitive mechanical ear, is that it sounds like a bag of spanners at full throttle.

MIne planes easily 3 adults up plus shopping. It also can tow a kid on a wake board.
 
tys all , how would one recommend a heavy outboard on a transom , pretty standard tubes as far as I can tell , there does not seem to be a board that will take the weight as I have searched all over , I can use the Mizzen as a pulley and put it into the locker , but this seems a pain every time , how do others store their larger engines , sorry this is a new boat to me , the engine was always on the dinghy and in the pontoon beside the boat so I dont know how the previous owners had the set up but there was no engine mount,
Opps sorry need to add there is no Davits the Dinghy get mounted forward , but the engine will still need to come off.
 
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good luck with shifting a 15 hp yamaha about while afloat------i have got one- weighs 50 kg----might have to compromise/balance speed of tender versus ease of manhandling lower powered lighter outboard
 
lenten said:
good luck with shifting a 15 hp yamaha about while afloat------i have got one- weighs 50 kg----might have to compromise/balance speed of tender versus ease of manhandling lower powered lighter outboard
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Yes I think you are onto something to old for moving it around all the time :D
thanks all for the input
 
FlyingGoose said:
Yes I think you are onto something to old for moving it around all the time :D
thanks all for the input
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I have a slightly bigger tender which is ideal with a 15hp. Works great two-up (total wgt 135kg) with an 8hp Yam, and I use the old 2-stroke version as it is only about 27kg. More than two people - esp if heavy - and it gets iffy, sometimes getting up on a plane with a following wind and slight sea, but mostly not.

But, in line lenten’s comments I compromised with an 8hp because of weight. As a matter of interest, how did you handle the 15hp wgt wise? Guessing it was 2-stroke?
 
We have a 9.5 ALU AB with a 15 HP Yamaha Enduro (2 strokes). Relatively light for the HP but great to have when the anchorage is distant or when 3 up aboard. It is our "daily driver" and gets much use. I doubt you could buy a 2 stroke in UK. If I had to do it again, Tohatsu would be a consideration.

Good luck.
 
Its worth bearing in mind that a 8hp 2 stroke develops more power than the equivalent 4 stroke - I was told by a very reputable dealer in Falmouth that to get the same power from my 8hp Yamaha 2 stroke I would need a 15/20hp four stroke. Just the weight of something like that put me off!
 
dom said:
I have a slightly bigger tender which is ideal with a 15hp. Works great two-up (total wgt 135kg) with an 8hp Yam, and I use the old 2-stroke version as it is only about 27kg. More than two people - esp if heavy - and it gets iffy, sometimes getting up on a plane with a following wind and slight sea, but mostly not.

But, in line lenten’s comments I compromised with an 8hp because of weight. As a matter of interest, how did you handle the 15hp wgt wise? Guessing it was 2-stroke?
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Never took it of the dingy to heavy , hence the dingy and outboard were on the pontoon beside the boat when i bought the lot , I can only asume they used the Mizzen to load the engine up and into the large locker,
But the thief managed to haul it up a stone wall beside a load of flats and 2 Cameras on the Estate , and no one seen or heard anything ,
My own fault thinking it was safe were it was , you live and learn :disgust:
 
FlyingGoose said:
Never took it of the dingy to heavy , hence the dingy and outboard were on the pontoon beside the boat when i bought the lot , I can only asume they used the Mizzen to load the engine up and into the large locker,
But the thief managed to haul it up a stone wall beside a load of flats and 2 Cameras on the Estate , and no one seen or heard anything ,
My own fault thinking it was safe were it was , you live and learn :disgust:
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That’s so irritating! Moving forward, I don’t know if you’re more Icelandic strongman or marathon runner, but if close to other boats I’d see how you get along lifting and manhandling other people’s outboards, and then see if you can borrow the ones you are comfortable with for a quick test on your boat.

The last thing you want is to do your back in on the first day of a cruise with the wife, kids, and mutts all shaking their heads! :ambivalence:

Edit: and don’t forget your ability to pull the entire kit up and down a beach for maybe 100m or more depending on tides.
 
A good rule of thumb is 5hp per adult but depends a little on the dinghy. Personally, i would never want a four stroke engine. Had one and that was enough. We have a 9.8 Tohatsu and a Yam 15 Enduro. We use the 9.8 in less secure dinghy docks and the 15 when we have to go longer distances or have four in the dinghy. 9.8 is very ecenomical. 15 isnt! 15 hp will tow a wakeboard.
We dont have davits. At night we haul the dinghy up the side of the boat with the spinnaker halyard. Its sits on a pair of fenders against the guardwires. Nice and high keeps it clear of thieves. To take the engine on and off we leave it lifted up the side of the yacht then attach the main halyard to the engine lifting strop and winch the engine off the dinghy. With one person on the winch at the mast and the other walking the engine on the halyard to the engine bracket on the stern you can easily move the engine.
 
You are fortunate you have a bit of length on this model.
I reckon a good late 2 stroke model of even an 8hp, ideally 10-15 will be ideal.

The Yamaha 8hp weighs almost exactly the same as a 4hp 4 stroke model.

I use an 8hp on a 3m rib and it will certainly plane with 2 adults and 1 child.

I did have a 10hp on a 3m valiant rib with remotes. That would plane with 2 adults and 2 kids. With one adult at the helm it would tow an inflatable ring and a knee board. It would run about 20mph.
This was a 2 stroke mariner 10hp.

I mention about the length because I also have a shorter 2.7m rib that won’t plane with the same 8hp and even just 2 adults. More length an hull area on the water is key with these wee things.
 
Slight thread drift so apologies.
Can anyone explain why a 5hp 2 stroke produces more oomph than a 5hp 4 stroke. From my experience they definitely do but I've always struggled to explain why.
 
In the OP's position I'd be looking at whether 2smokes were still available in the channel islands. And if they are, I'd be ordering myself a Tohatsu 9.8 and planning a trip down to pick it up.

They're cracking wee things and a good compromise between power and weight.
 
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