Aux engine size

[Tim M]

This has been asked before, but in the name of clarity.....

Is a 3.3hp aux engine likely to be of any use on a 5.6 RIB?

[ADS]

Originally Posted by Tim M

This has been asked before, but in the name of clarity.....

Is a 3.3hp aux engine likely to be of any use on a 5.6 RIB?

Would probably just about push it along, although the rule is 1hp/m. The main issue is tides and currents, I motored my parent's 29ft sailing cruiser from one berth in st vaast marina to another with a Yamaha Malta 3.5hp, I didn't even need to go flat out and that was fine, stopping 3 1/2 tons of yacht however was not going to happen!
I would get a 4HP minimum Tim because then you get a proper reverse as well, you may not have room to spin a 3.3hp round on your transom to reverse.

[Simon Hodder]

We run a Mercury 4 hp auxillary on our 5.5 metre Humber, and although we've never had to use it in anger, we've always been impressed with it's performance when we've used it to give it a bit of a run. It's prooved very handy when crossing really shallow patches of water, too.

[Tim M]

I hope never to have to use this in an emergancy situation. But, say if the main engine cuts out for what ever reason at the enterance to the harbour or in front of an on-coming ship it would be nice to know I could get out of the way relativly easily. Plus I was thinking it would be a lot more suitable for when I want to use the RIB on the river....

[BogMonster]

The guy I bought my 5.8 from told me his 4hp Mariner aux (which I didn't get) was ok for up to about 5 knots in calm conditions but that rapidly become not many knots at all into any kind of headwind or into any sea. So I have just ordered a 6hp Suzuki 4 stroke for my aux which I hope will do the job.

Edited to say that just for info I found out that the Johnson and Suzuki engines in that size range are all made by Suzuki and the 4, 5 and 6hp 4 strokes are all basically the same engine just with a different carb, so the 6hp is quite a light engine about 26kg I think for the long shaft one. Got mine from Outboards Direct, Charles Oakley is a bugger to get hold of by email but a very very helpful chap when you eventually do!

[hobnob]

I’ll probably get flamed for my first post here, but anyway…

Thrust is not equivalent to horsepower. This is the principle behind ‘SailDrive’ engines, which get mentioned elsewhere on this forum. They have two engineering differences from a conventional outboard: a lower gear ratio, and a larger propellor.

This enables the saildrive engine to move more water, albeit at a lower speed, than a conventional engine. This is suited for larger hulls.

I have just obtained a Seagull 102 for my RIB auxiliary [gasps of horror]. Why?
1) When I put a Honda 5hp 4-T into the RIB, the vibration made it lose gear oil.
2) It has a 13” prop and is designed to move 10 tons plus of canal barge.
3) The Seagull is serviceable at sea
4) It was cheap!

There are downsides, but as a Seagull owner before I feel I can deal with them.

Regards,

Tim