How much thrust from a 4hp sailmaster?

[jackle61]

I recently received a mid-eighties 4hp sailmaster, and although they aren't usually rated by pounds of thrust (like electric trolling motors) I am wondering if I wouldn't be better off selling the 4hp and buying a trolling motor. It would be used for periodic trolling on a 24' pontoon. I realize it also depends what prop I'm running on it. I just can't find any sort of comparison between hp and lbs. of thrust. Any ideas??

 

[samo_ott]

Re: How much thrust from a 4hp sailmaster?

4hp ~= 3kw for all it's worth.

 

[trendsetter240]

Re: How much thrust from a 4hp sailmaster?

I recently received a mid-eighties 4hp sailmaster, and although they aren't usually rated by pounds of thrust (like electric trolling motors) I am wondering if I wouldn't be better off selling the 4hp and buying a trolling motor. It would be used for periodic trolling on a 24' pontoon. I realize it also depends what prop I'm running on it. I just can't find any sort of comparison between hp and lbs. of thrust. Any ideas??

This is something I have also wondered myself many times. I've even seen a few threads on this topic on this board over the past 2 years. The end result is there really is no concrete way to convert hp rating to thrust in foot/lbs. Or at least noone I know or have seen on here can do it!

An electric trolling motor will be much quieter but will require a large battery (or two) that needs to be recharged frequently. Also you will get far less range out of the electric than the 4hp gas motor.

The only reason i'd say to get an electric for that pontoon is if you want to troll in absolute silence and don't mind moving very slowly. Otherwise stick with the gas kicker. I love my 4hp evinrude, just wish it had an alternator to power my electronics while im trolling.

Cheers

 

[ONERCBOATER]

Re: How much thrust from a 4hp sailmaster?

i am not a guru on this, but i think the best way and what approach this question is to ask what pitch propeller you have now? And then look at the available props for that model, assuming it is an 84 since you said mid 80's you would have 7.5x6 7.5x6.5 and 7.5x7.5 and they go somewhere between $30 and $90 ea. (as that is what i found available in a 2min search just now) as you change pitches you would change how much water the engine tries to move with ea revolution of the prop. my guess is the lowest pitch prop you could find for that engine would be the most effective for moving the pontoon boat and not lugging the engine. Theoretically as you drop in pitch you will gain in thrust but lose potential velocity.

if i had to make a wild guess i would expect somewhere between 260 and 300lbs thrust from a 4hp.... but that is a wild guess and honestly i have nothing to base it on but gut feeling and iffy information i have gleaned from the net that was someone elses guess or estimate.

The plus side at least from my perspective is you would be just sipping gas while trolling with the lil 4hp and would have the ability to likely troll all day on 6 gal of gas or less. To move a pontoon boat with electric trolling motor for several hrs would very likely drain a battery or batteries very quickly i would likely opt for the small gas engine for most trolling duties.

if you could get a lower pitch than 6 it might be better as a pontoon boat is a large amount of drag to say the least.

with the exception of the prop prices and pitches that i found available, all the other info is guestimates based on 1 amp per pound of thrust for a trolling motor so 12v x 80A would be 1160kw and 80lbs thrust (theoretically) so best guess would be 300lbs thrust with the right prop. I am sure that there are losses to be accounted for in the gear train.

someone most likely would have a better answer than this. as this is just extrapolated data from guesses and estimates of others that i have seen.

sean