prop size

i have a 1988 50hp vro evinrude motor on a fibreglass 15ft foot boat. Basically i believe the prop size is wrong because when fully loaded up with gear 4 people and dive gear it struggles big time and it also is eihter to fast for the conditions or too slow making it very uncomfortable and annoying. at the moment i have a 11-3/4 x 17 but i dont understand the sizing. i am basically looking for a prop with more torque

Re: prop size

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Re: prop size

danieldohrman said:

i have a 1988 50hp

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That is not a lot of motor, but should do ok. 4 people and dive gear sounds like you are at the high limit of that boat so you may want to consider a bigger one or less gear and such.

at the moment i have a 11-3/4 x 17 but i dont understand the sizing. i am basically looking for a prop with more torque

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11-3/4 is the dia of the prop. Thats easy.
17p is the pitch. This is the business end and the number you are looking at. In theroy, this prop will move 17" forward for every complete revolution. Now minus 10% for average slip and you end up with 15.3" of forward motion.
Like Bond-o says you will need to do some reading so stuff like this makes sense.
Then you need to read posts that have tested props and test your boat, loaded, empty and what you consider a normal load. Data will contain RPM's at "X" MPH. Post this and also what issue you are trying to correct.
That will give us and you a good starting point to help you.

Re: prop size

the issue im having is that my boat doesnt appear to have enough power and bogs down lots. it has an aliminuim 11-3/4 x 17 prop unsure of the manufacturer. basically my boat tops out 55kmh which is way to fast for the condition i travel in 40kmh tops averaging 30kmh. but the boat doesnt want to sit at this speed it either for 40 or 20 kmh my boat is a waverider with a 50 hp evinrude vro motor. also my boat porpoises and i have tried adjusting the hieght of the motor and this didnt stop it

thanks daniel

Re: prop size

55km is a good speed so I think you have adaquate power.What is the rpm at max speed?
The boat may be stern heavy.Do you have gas and batteries in the stern?
Move something forward.Even people if possible.
Boat may also have absorbed water in the foam under the floor.Does it seem to sit low in the stern at rest?
If it porpoises it may be trimmed out too far(prop away from the boat).This would also make it fall off plane easily.Trim in( prop closer to boat)a little, one notch if manual trim.
A 4 blade prop will plane easier and stay on plane with less throttle.
Trim tabs like Smart tabs will also help.