alahol2
Well-Known Member
For many years we ran a Yam 9.9 longshaft with remote throttle and gears, which could be connected to the steering, on a 32ft cat. I can genuinely say that I never once wished for more power. They are brilliant engines.
Help with outboard choice for yacht, please.
- Thread starter StUrrock
- Start date
StUrrock
Well-Known Member
Thanks for the tip.If you can connect the motor to the steering, it should just be a matter of a little practice. That really will make a world of difference. Also, most 28ft boats these days have more than 10hp. Ours probably originally came with a 9.9, but nearly all are now running 15hp. I would guess your displacement is more than ours, that’s more mass to start and stop, though be grateful you don’t have 3 hulls for windage
The Yamaha 9.9 HT really does seem to have the attributes with the better gearing and huge prop for low speed work. However, been looking at the Tohatsu new EFI models, they are so light and good price. Their 15HP looks like a contender even though the gearing and prop size is not as good as the Yam. With 15 horses on a longer shaft surely astern manoeuvres will be a source of pleasure soon!
Refueler
Well-Known Member
The best O/B for such a boat ?
Mercury Saildrive Outboard .... it has a different gearbox ratio and prop designed specifically for yachts ...
I went through Yamaha's .... and various others - but once I got that Mercury - WOW ... what a difference.
I suspect that they can only be found 2nd hand now as they are 2str .. and I doubt any are made now.
Mercury Saildrive Outboard .... it has a different gearbox ratio and prop designed specifically for yachts ...
I went through Yamaha's .... and various others - but once I got that Mercury - WOW ... what a difference.
I suspect that they can only be found 2nd hand now as they are 2str .. and I doubt any are made now.
SeasickPete
Active Member
Hi, you also might want to have a look at a Suzuki or Tohatsu 9.9, not the 9.8. Because the 9.9 is fuel injected, so no more issues with clogged carbs. The 9.9 is also sold as 15 and 20 hp which are electronically limited and have a reducer in the intake but otherwise the same motors.
fredrussell
Well-Known Member
So does the Yamaha most on this thread are recommending! Actually, there was a time when Mercury OBs were rebadged Yamaha ones. I think these days most of the small-ish Mercury, Mariner etc are made by Tohatsu - it’s confusing.
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StUrrock
Well-Known Member
Hi All and thanks for all your expert advice.
After communicating with over a dozen dealers only 2 bothered to come back to me and only one of those was really helpful with advice etc. who was not a Yamaha dealer.
So we are going with a 15HP 4 stroke long shaft tiller version with high thrust prop, but with remote controls attached.
Our current 2 stroke ventilation plate is 2 inches below the water line on our 15inch transom, so feel sure the extra few inches of the long shaft will help greatly with bigger seas and going astern. Another good thing with the Tohatsu is that we could make it extra long shaft later with a kit should we need even longer!
After communicating with over a dozen dealers only 2 bothered to come back to me and only one of those was really helpful with advice etc. who was not a Yamaha dealer.
So we are going with a 15HP 4 stroke long shaft tiller version with high thrust prop, but with remote controls attached.
Our current 2 stroke ventilation plate is 2 inches below the water line on our 15inch transom, so feel sure the extra few inches of the long shaft will help greatly with bigger seas and going astern. Another good thing with the Tohatsu is that we could make it extra long shaft later with a kit should we need even longer!
Chiara’s slave
Well-Known Member
Sounds like a good result. The other thing you can play with is of course the prop. But definitely go with a helpful dealers recommendation first, it may well be spot on.
Blueboatman
Well-Known Member
Well chosen. Plenty of reserve oomph and push.
If you find yourself pulling up the anchor standing on the foredeck in a bit of a lumpy sea and you hear the exhaust note from the outboard a bit too much in air and not submerged very much in water(!) , then that is one indication that you may want the outboard leg to be a tad longer but I’m sure it will be fine as is.
I like Tohatsu, they made lots of the smaller rebadged ones.
And a mate used a Toh 8hp on a side deck bracket to move an old 40ft meter boat in and out of harbour back in the day!
If you find yourself pulling up the anchor standing on the foredeck in a bit of a lumpy sea and you hear the exhaust note from the outboard a bit too much in air and not submerged very much in water(!) , then that is one indication that you may want the outboard leg to be a tad longer but I’m sure it will be fine as is.
I like Tohatsu, they made lots of the smaller rebadged ones.
And a mate used a Toh 8hp on a side deck bracket to move an old 40ft meter boat in and out of harbour back in the day!
Refueler
Well-Known Member
Most Outboards can have Extra length added to extend more than standard long shaft ...
Obviously the question is availability of kits.
Tranona
Well-Known Member
No need for that. As he says the transom was made for a standard 15" shaft motor, so a 21" long shaft will get the prop 6" lower in the water. Downside is increase in weight and greater protusion when tilted and sailing.
Personally I think a 15hp is way OTT. The boat is a lightweight cruiser/racer with a displacement of around 1700kgs. It only requires 8hp to get hull speed of around 7 knots. A 15hp is a waste. The 9.9 Yamaha high thrust originally suggested is probably a much better choice with more than enough power and a 12" prop. Quick calculation suggests a prop size of between 11 and 12".
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StUrrock
Well-Known Member
Totally appreciate that, just all the Yam dealers I spoke to 3 in total didn’t give a sh*t!
Additionally I got quite a shock how light the 15HP Tohatsu is, the lightest version is 43KG, whereas the Yam is 44KG!!
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Tranona
Well-Known Member
Does not seem a sound reason for buying an engine that is not appropriate for your boat. The Tohatsu is designed for small planing inflatables and RIBs.. You simply won't be able to use the power the engine can produce and it will not do the job you want of having greater stopping power at low speeds. Powering displacement boats is all about the propeller and not what powers it and a large slow turning prop such as the Yamaha has is exactly what you want. 8hp is all that is required to get hull speed and I would estimate the Yamaha will give you around 7,5 knots with comfortable cruising at around half throttle.
Chiara’s slave
Well-Known Member
The guy has made his choice. It will be fine. Great even. Nothing wrong. Nothing at all. We have a Honda 15, it’s measurably better than the Yam 9.9 it replaced, with similar displacement, though obviously our prismatic is vastly different. We corrected it’s only flaw with the right prop. Our friend here has already done that with the help of the dealer, might well be a hole in 1. It’s fine. Oh, did I mention, he’ll be ok?
Refueler
Well-Known Member
I have to agree with Tranona - a displacement boat requires Thrust ... not Revs. OK with the change from 2str to 4str - that has closed the gap somewhat due to the lower rpm etc ... but still holds true.
IF the dealer is swapping the prop to suit the boat and engine is OK with it - then why not ?
When I changed from a Yamaha normal O/B to the Mercury Saildrive O/B of similar HP .... the difference was astounding.... the 'bite' of the Mercury was literally instant instead of the few seconds thrashing of the Yam ...
IF the dealer is swapping the prop to suit the boat and engine is OK with it - then why not ?
When I changed from a Yamaha normal O/B to the Mercury Saildrive O/B of similar HP .... the difference was astounding.... the 'bite' of the Mercury was literally instant instead of the few seconds thrashing of the Yam ...
Chiara’s slave
Well-Known Member
And we got exactly that by changing prop. Blade area, diameter and pitch can all be arranged to suit the application, and most outboards can accommodate a larger prop than the one they came with. Maybe thats why the dealer recommended a Tohatsu, maybe he knows something about them that we don’t. As I say, our Honda behaves perfectly well on our boat of similar displacement. Theres no magic about saildrive outboards apart from often, not always, a 10% lower drive ratio and that crucial clearance for a larger diameter prop. Ghat last being the big one. If the Tohatsu, like the Honda, can be re propped to suit, then why the hell not.
Tranona
Well-Known Member
There is more to it than just the size of the prop. The other key piece of information is the shaft speed - function of the maximum revs and reduction ratio. Typically for displacement yacht auxiliaries you need a large slow turning propeller and shaft speeds are commonly in the 1400- 1800rpm range and for a 10hp motor the typical propeller size will be 11 or 12" diameter and for a 15hp 13" diameter.
Now take the two engines under consideration. The boat needs 8hp to get hull speed of around 6.7 knots and 5hp for 6 knots cruising.
The 15 hp Tohatsu has a maximum revs of 5500 (mid of working max) and a reduction ratio of 2.15 giving a shaft speed of 2560 rpm. The calculated prop size is 9*6"
The Yamaha 9.9 High Thrust also has a working max of 5500 BUT a reduction ratio of 2.92 giving a shaft speed of 1880 . The calculated prop size is 11*7"
Hopefully you will now appreciate why the Yamaha is the engine of choice and why it is so highly regarded. It was designed to replicate the characteristics of a small inboard diesel. Run the numbers with a Beta 10 and a TMC 2:1 box and you get a recommendation of 11*8" reflecting the slightly lower shaft speed compared with the Yamaha.
The Tohatsu with its smaller higher revving prop will not solve the OPs problems of poor control at low speed although it will make the boat go faster even though it will never get anywhere near maximum output.
BTW your Honda has similar characteristics to the Tohatsu. It is made to power small inflatables and RIBs and is severely compromised when powering low speed (less than 7 knots) displacement boats.
Refueler
Well-Known Member
The Mercury 7.5 and 9,9 Saildrive outboards were distinctive by their weight ! This was due to the different gearbox / leg fitted ....
But the difference in use was amazing ... just a pain to lift on / off
ontheplane
Well-Known Member
I do also think a High Thrust Yam would be better than a standard Tohatsu even with a modified prop....
But hopefully it will all be ok.
But hopefully it will all be ok.
Blueboatman
Well-Known Member
Those numbers are convincing..
Oh oh
Maybe the tonatsu deal hasn’t been finalised yet?
StUrrock
Well-Known Member
Fitted the Tohastsu yesterday, pleased with initial results.
Will give an in depth review later.
Will give an in depth review later.