F-Ribs And Sibs - Inflatable Boat Community

Looking to buy or bought your boat and now you need an outboard to power it but which one do you need? Here’s some information which may help you make the right choice.

The most import decisions to make are:
1. What is the maximum HP (horse power) and outboard weight your boat can take (this information is available on the identification plate on the transom of your boat)?
2. What shaft length fits the transom on your boat?
3. What weight is the outboard and will you be able to man-handle it?

If you are completely new to boating and are looking to buy an outboard for your boat you’ll need to know what all this new terminology means. One of the biggest and most costly mistakes made is not knowing which length of ‘leg’ or shaft outboard you require to suit your boat. This particularly applies if you are buying second hand as often the seller is as confused as you are!

Below is a guide to an outboards layout
Most, if not all boat manufactures will require the anti-ventilation/cavitation plate of your mounted outboard to be level with the bottom of your boats keel or to a maximum of 1” (25mm) below to get the best performance.
Mounting it too high can result in the propeller not being fully submerged in the water causing it to draw in air (cavitation) resulting in loss of drive/momentum and loss of steering. This can also cause the engine to overheat as the water intake will suck air instead of the cooling water required, resulting in engine damage!!
Mounting it too low can cause extra drag with loss of speed and heavier steering.

The diagram below gives you the measurement you need to take to fit the correct length of shaft to your boat. If the correct height cannot be achieved with the bracket sitting onto the transom you can do a bit of ‘fine tuning’ by using a ‘packing piece’ placed under the clamp bracket to raise it.
Lastly, it’s very tempting to go for the largest most powerful outboard for your boat, however the weight differences between 2 stroke and 4 stroke outboards are considerable for the same given hp.
For example a Tohatsu 15hp or 20hp 4 stroke outboard weighs 52kg but a 2 stroke 15hp or 20hp outboard weighs 39kg however sales of new 2 strokes for ‘pleasure use’ ceased in December 2006 so you’ll be shopping for a used second hand 2 stroke outboard if you want one or consider a 10hp 4 stroke instead at 38kg.

Hope this helps and happy hunting.

I could have done with all that info a few months ago lol, Superb post as ever Paul...
I bought a Suzuki 15hp 4 stroke from Pennine Marine, Peter up there seems a superb and knowledgeable chap.

To me the most important thing about buying an outboard for an sib is weight. Can you physically lift the motor. Will you hurt yourself setting the motor in your automobile and then on your transom. Go down to a dealer and pick up the motor and see how it feels. If you can't do that then go to a gym and pick up some Dumbbells that weigh the same as your outboard. You will know right away what you can and can't lift. You need to buy the biggest motor that you can physically handle. If you buy to small of an outboard you will be bored with the slow speeds. If you Buy a motor that is to heavy and throw your back out you will soon find yourself looking for a new hobby. If possible try to find a good 2 stroke motor. They are much easier to maintain and can be transported in any position. 4 strokes are physically larger and heavier and have transportation restrictions. If you buy a Yamaha 2stroke the the oil is mixed 100 to 1 so smoke will not be an issue. They burn very clean. A lot of people sell their sib's because it's just to much of a hassle because it's just more than they can handle.

To me the holy grail of sib outboardsfor people who do not trailer is the Yamaha 2stroke 15hp. It only weighs 79 pounds and will move just about any SiB as fast as you need to go. It's super reliable and parts are readily available. This motor can still be purchased new in the Caribbean, Bahamas, and Mexico. Search your local classifieds religiously and one will eventually turn up. If you plan on trailering than disregard everything you just read. See ya on the water.

Very useful to know before I go spending the hard earned. Thanks .

Johnm0asn wrote: ↑

06 May 2020, 19:36

Very useful to know before I go spending the hard earned. Thanks .

Bear in mind that the new models of 4 stroke motors are lighter now - my Tohatsu 20hp efi weighs 43Kg Suzuki is similar, just choose any of the modern ones that can be serviced by a dealer near to you

Indeed Warder, Good to raise the weight subject again as at the time of writing the lightest outboard was about 52kg..
Substantially less now!
Images re-added on first post, for some reason they failed to display....

Martin

Hi guys I’m about to push the button for a new 15hp 4 stroke had settled on the Mercury due to having the improved tiller handle over the Tohatsu (know basically the same engine) but have been told today by another “siber” they had been advised to steer clear Of Tohatsu/Mercury and go for the Suzuki now I don’t know which way to go as spending 2K on a new engine I would like to get the best I can

High MarkyP and to the forum.

I have the Suzuki and I do feel that it is the best small engine out there but there is nothing wrong with any of the engines from the big 4: Suzuki, Mercury/Mariner, Tohatsu and Yamaha. I very nearly bought the Mercury/Mariner 20 as I love the tiller on them, but the slightly lighter and easier to start Suzuki won out for me in the end.

The only real advantage of the Suzuki is that it had a slightly larger AV plate which makes it less prone to ventilation on the Honwave T38, and that’s only an issue if you have a T38.

Personally, unless your boat limits you to 15hp I would get the 20hp variant as they are the same weight and 33% more powerful.

Hi Chris Thanks for the info I’m limited to 15hp I also have a Honwave airdeck, it looks like a trip to a Suzuki dealer is in order to have a look then. Luckily I’ve found one nearby Regards Mark

Hi MarkyP, you should ask the other "siber" - if Tohatsu are so bad, why do other manufacturers (Including Yamaha and Mercury/Mariner) rebadge Tohatsu engines and sell as their own?
You may have guessed by now - I'm a VERY happy Tohatsu owner 43Kg 20hp efi, smooth, quiet and frugal.
OK toys are back in the pram