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Old 14 August 2005, 04:47   #1
Country: UK - England
Town: Carterton, Oxon
Boat name: Trigger's Broom
Make: Lomac
Length: 4m +
Engine: Yamaha 40
Join Date: Jul 2003
Posts: 250
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Auxilliary Engine

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

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Old 14 August 2005, 10:19   #2
Country: UK - Wales
Town: Milford Haven
Boat name: Various
Make: Commercial
Length: 10m +
Engine: Screw / Voith / Jets
Join Date: Sep 2002
Posts: 791
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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.


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Old 18 August 2005, 12:29   #3
Country: UK - Scotland
Length: no boat
Join Date: Aug 2005
Posts: 21
honda 8hps are small,powerfull and apparently reliable, they might well get you home against the tide and wind
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Old 22 August 2005, 15:13   #4
Country: UK - England
Town: Towcester
Boat name: TBA
Make: Delta
Length: 6m +
Engine: Suzuki 175
Join Date: Nov 2002
Posts: 328
dont skrimp on the 'wing' engine

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.

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Old 22 August 2005, 15:20   #5
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Country: UK - England
Town: Berkshire and Devon
Make: Lodestar
Length: under 3m
Engine: Mercury 5hp
Join Date: Jul 2002
Posts: 5,015
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.
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