A question of power ?

Posted: Tue Dec 15, 2009 11:38 am

Hi this may be a stupid question but here goes I have a boat with a 8hp inboard engine which drives a propeller that has an overall radios of about a foot. On outboard engine I have seen the propeller has a smaller overall radios but the engine has a larger hp does this mean that my set up has as much push as a larger hp outboard engine as turn for turn my one will push more water.

i hope someone can answer this for me thanks.

Posted: Tue Dec 15, 2009 1:10 pm

Simple answer is no. The pitch and diameter of the prop is in direct relation to the power of the engine and the reduction ratio of the gearbox. This gearbox ratio and the hull design of the boat determins the size of the prop required. Outboards are revvy little rascals and require a far diffferent gearing and prop to your inboard unit.

Posted: Tue Dec 15, 2009 3:05 pm

even i couldnt have answered as well as that

Posted: Tue Dec 15, 2009 9:56 pm

thank you for your answers is there a way to work out the amount of push or would it be thrust my boat has the reason for my qestion is i lanch my boat from a beach when we went out the trailer was backed into the sea and off we went no problems on coming back we were told that we may have a problem getting off the beach if there is a bit of a swell as we would not have the power to get ourselfs out of the surf before we had been washed back onto the beach. can you shed any light on this. once again thank you for your last answer and i hope you can answer this one for me.

Posted: Tue Dec 15, 2009 10:09 pm

Again the answer is no!
Even if the thrust your engine/gearbox prop combination could be calculated into pounds of thrust, the number obtained would have no meaning in relation to your problem. How many pounds of thrust are needed for your particular location in particular tidal conditions? There isn't a definitive number.
Be guided by those who use the beach regularly and are aware of local conditions. The danger along the surf line is the wave action turning the boat side on to the waves and becoming swamped or overturned on the shallow shoreline.

Posted: Tue Dec 15, 2009 11:50 pm

Thanks again for your reply this boat fishing is not as easy as just dropping a boat in the sea is it.

Posted: Fri Dec 18, 2009 11:26 am

Nearer 20 hp would be better against strong tides and swells.But swapping inboards can get costly and as you have two auxilary outboards if one of them is 6 or 8hp then fire that up as well i know its only a temporary measure but it may help

Posted: Fri Dec 18, 2009 1:32 pm

and then envy your pals by saying you have a boat with twin engines devil