What size Donkey Engine on a 5.8 Rib?

[HoveRuss]

Would really like to grab a backup motor for my boat. In order to get something that actually moves it enough to get me home, can anyone advise me what size motor would suit?

Cheers

[chewy]

15hp would do, are you leaving it mounted on the transom?

[Steve_B]

I think you will need 6HP minimum, to give you some headway and therefore steerage.

As a stand by, the make will depend on your budget or what is available. Most are very reliable these days. As it is now end of season, there should be some good bargains to be had if you haggle

[HoveRuss]

Originally Posted by chewy

15hp would do, are you leaving it mounted on the transom?

Thats the plan. Thats a big lump tho isn't it?

[chewy]

Yep, depends how fast you want to go though?

[HoveRuss]

Fair comment!

[J S]

you would only ever go so fast with an aux engine due to the displacement speed of the hull. so a 40hp aux wouldnt be any faster than a 15hp one it would just make more noise and wash.

James

[Poly]

Originally Posted by J S

you would only ever go so fast with an aux engine due to the displacement speed of the hull. so a 40hp aux wouldnt be any faster than a 15hp one it would just make more noise and wash.

James

I'd expect a 40HP on a 5.8m boat to get on the plane with the right prop...

[J S]

Originally Posted by Polwart

I'd expect a 40HP on a 5.8m boat to get on the plane with the right prop...

Yes i was maybe exaggerating a little, but where it would be mounted the prop would probably end up out of the water when planing.

James

[Chris]

I had a 4hp Yamaha Longshaft on my old 5.25 Viper. I sourced a lower pitch prop for it and managed to get about 4knots sometimes 5. It was enough to get you way from trouble if the main cuts out near some rocks but it would be a long ride home

I kept mine mounted directly on the transom which is the best place for it (don't like the brackets), however do make sure you maintain it as its going to get wet every time you go out even if you dont use it and you will also need to improvise a way to secure it well as the saddle barckets on the smaller engine don't take much of a pounding.

Having an internal fuel tank is handy as when you want an aux its generally going to be in a hurry, so hooking up a fuel tank and trying to measure oil into a jerry can when you are in an F6 200 yards from the breakers is not a great situation to be in

I always made it a habit to run mine at least every other journey to make sure it was going to work when I needed it to.

[biffer]

general rule of thumb for ribs, 1 horse power per metre, 6 metre 6 hp close enough, you'll make headway, but hopefully you shouldn't need it