Auxilliary Engine

[Noddy]

Can anyone advise on what would be an ideal size for an auxilliary outboard for my 4.65 Batt Rib? I have a bracket already fitted. Weight is at a premium - normally cruise solent area so just want a "get me home" option
Thanks
Martyn

[Alex Brown]

I think a general rule is normally about 1hp per metre of boat for aux engine.

I didn't go by that, and put a 4hp engine on the back of my boat - it was used today to get me to safe anchorage out of the channel to fix fuel problems on the main engine.... 3.5knots against the wind wasn't too bad I didn't think.

-Alex

[RESCUE1]

honda 8hps are small,powerfull and apparently reliable, they might well get you home against the tide and wind

[Paul Beaurain]

We have a 6.3m Humber with 6Hp suzuki aux.

I always run it on each trip - usually for a few minutes while in the harbour or river. 3.5 knts is max when calm.

Leg failed on main Suzuki 115 on way back from Fowey to Poole (off swanage) be assured 6Hp was insufficent to avoid a call to the coastgaurd.

Aslo take care that the Aux shaft is long enough to clear the hull. The prop can be very inefficent if partly masked by the transom.

Next boat will be 7.5m with 200 or 250 main and aux will be 25Hp.

Paul

[Richard B]

Originally Posted by Paul Beaurain

aux will be 25Hp.

Paul, don't forget the law of diminishing returns... you may find that anyting over 15hp just doesn't get you any faster as you're limited at displacement speed by the hull length equation, ie about 8kts for a 7m boat.