18hp Tohatsu on max rated 15hp SIB

wxmrich · 17 July 2012, 20:59

I've just bought an 18hp 2-stroke Tohatsu for my 3.3m SIB.

I was looking for a 15hp but at £670 I think I've had a bargain?!!

Anyway, I'm hoping for some reassurance that the engine will be ok on my SIB max rated 15hp. It's the 41kg model so I imagine weight isn't the issue?

Boats&Outboards · 17 July 2012, 21:02

No chance! It will be dangerous and I strongly advise you to stick to the ratings. You've wasted your money. That being said.... I guess I can give you £750 for it if it gets you out of trouble

Peter @ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

Landlockedpirate · 17 July 2012, 21:19

Great buy, I was tempted but couldnt think of an excuse for Wifey if I bought another engine !

In practical terms there will be no problem using a slightly over sized engine, the transom wont fall off and the boat wont shred its self.

But a couple of words of caution. An oversized engine could invalidate your insurance and if you are lightly loaded and going into a head wind, keep as much weight forward as possible.

willk · 17 July 2012, 21:42

Lucky git. You MIGHT want to clear it with the Insurance company, but I can't see it doing the SIB any harm. Of course, if the transom falls off, I've never heard of you

SIBer · 18 July 2012, 20:07

That 18 is going to push you into the middle of next week on a 3.3m

wxmrich · 19 July 2012, 08:34

Thanks for the replies, it seems I should be using it with plenty of caution!

Will definitely be taking it slow first time out.

awa154 · 22 July 2012, 10:36

Is the weight of an 18hp greater than a 15? If not, there shouldn't be a problem as, unless you're running it at full throttle, you wont be using 18hp anyway.

Personally, I would've thought 15hp was overkill for a 3.2 boat. Unless you are going to be loaded to the max.

prairie tuber · 22 July 2012, 16:19

I don't think you have anything to worry about. Drive according to the water conditions and have fun.

As an aside, I have an old zodiac Mark 1c, which is about 3.3m which is rated for a max of 25 hp. With a 25hp motor and a light load, you would only run at WOT if on glass smooth water. With even slightly choppy water, cranking the throttle could easily bounce you out of the boat.

wxmrich · 22 July 2012, 19:05

The max engine weight for the boat is 55kg, which I imagine is the heaviest of 4 stroke 15hps.

The Tohatsu I have is only 41kg so well within the max.

I'm just going to take it easy and judge the conditions/how the boat responds to the throttle. I won't be using it with any less than 1 other adult and a reasonable amount of gear anyway so I'll stick the weight forward to try it out.

chewy · 22 July 2012, 22:18

I'd be happy with it!

Salty · 23 July 2012, 19:52

I was very tempted to bid on that motor myself but already have a tohatsu 16 that Im going to use for this summer then maybe upgrade next year as I bought my honwave new a few months back so have to do things in stages or the misses will moan at me spending too much dosh?!

Looks like you had a bargain there though mate. My honwave t38 goes pretty well with my old HEAVY tohatsu 16 so yours should fly!

I live quite close to you. Drop me a pm if you ever fancy going out on both boats, safety in numbers and all that!

Salty

bingosucks · 24 July 2012, 15:52

i have a 2stroke 15 hp on a 3m boat 5hp over the limit but a 3.1m boat can take a 15 ??? yep i went through the same worries.... i have just managed to clock 24.9mph with 2 of us on and sat well up front, the scary bit was i could have turned a little bit more ;-O but bottled out due to the constraints of the water, it was the acceleration bit that took me by suprise . make sure you use a tiller extension and a life vest/bouyancy aid and turn the dial slowlllllyyyyy

MEE · 26 July 2012, 03:09

How old are the glue joint on the transom? I am restoring my older bombard and i was surprised. ... well shocked .... in how easy it was to peel the transom mounts from the tubes. If they are over ten years old i would check them closely before you stress them to there design limits on the water. Just sayn.

wxmrich · 27 July 2012, 08:39

Thanks guys,

Salty I'll PM you when I fancy a boating convoy, cheers!

Boat is about 8 years old but the engine didn't seem to put much strain on it last night on first try.

So first time out, just for a quick hour. Managed 22 mph on the GPS, that's with 25 stone of human and about 5 stone of gear/fuel.

Trim needs looking at, took on quite a bit of water from the engine splash. Would anything else cause this??

Felt safe the entire time even at full throttle but couldn't keep full throttle for long because of the splash problem.

willk · 27 July 2012, 09:51

Quote:

Originally Posted by wxmrich

Trim needs looking at, took on quite a bit of water from the engine splash. Would anything else cause this??

Height. It's a common enough problem. You could try raising the engine on the transom a bit, if there is enough play. Put a piece of timber under the saddle.

wxmrich · 27 July 2012, 10:05

How much height are we talking? An inch or so?

Thanks

willk · 27 July 2012, 10:12

As much as you can get while still having enough bracket securely clamped to the transom! It will probably end up as no more than an inch, but take as much as you can get. I think the problem is that these little boats are quite shallow transomed and some small outboards are quite "leggy" so sit a bit lower than is optimal. If you have much room to lift it, make sure that the
anti ventilation plate remains below the keel.

I raised mine about 30mm and it helped, but did not remove the problem totally.

wxmrich · 27 July 2012, 10:20

Ok thanks for the advice. Yeah the problem is probably the 17inch leg compared to the 15 on my small 4 stroke. I'll experiment with pieces of timber for the next trip.

Salty · 30 July 2012, 17:00

Quote:

Originally Posted by wxmrich

Thanks guys,

Salty I'll PM you when I fancy a boating convoy, cheers!

Boat is about 8 years old but the engine didn't seem to put much strain on it last night on first try.

So first time out, just for a quick hour. Managed 22 mph on the GPS, that's with 25 stone of human and about 5 stone of gear/fuel.

Trim needs looking at, took on quite a bit of water from the engine splash. Would anything else cause this??

Felt safe the entire time even at full throttle but couldn't keep full throttle for long because of the splash problem.

My Honwave has got some little triangular flaps either side of the outbord that attach to the top of the transom and tubes. Apparently this is to reduce water splashing over the transom. I dont seem to get much water in mine apart from if you come of the plane too fast and get a big surge of water, so maybe they do actually work?

Maybe you could cobble something similar up?

wxmrich · 30 July 2012, 17:53

Yea I've seen them on other SIBs and wondered if that's what they're for.

I'll try the blocks of wood to raise the transom an inch or so and if it's still spraying I'll look into that.

Saying that, the majority of the water appeared to be coming from directly between the clamps..