help and input on props

[jonbmx900]

hi all im new to this site and i have a 2003 14ft zodiac pro 7 with a suzuki 40 hp 4 stroke on it but it seems to rev out to early it seems to have the original factory prop on it still but when i brought the rib it came with another prop but i havent tried it yet and cant remember what the markings are on it but how much differance will a corser prop make to the revs and or top speed i know this is a bit vague but im new to this but really injoy it and am allready thinking of getting a bigger rib as i would like a bit more room and speed to

i would be greatfull fo any help and input on the above question also if i get a bigger rib should i go for another 4 stroke or a 2 stroke what are the pros and cons

with thanks jon

[Nos4r2]

Originally Posted by jonbmx900

hi all im new to this site and i have a 2003 14ft zodiac pro 7 with a suzuki 40 hp 4 stroke on it but it seems to rev out to early it seems to have the original factory prop on it still but when i brought the rib it came with another prop but i havent tried it yet and cant remember what the markings are on it but how much differance will a corser prop make to the revs and or top speed i know this is a bit vague

Welcome

Far too vague to be able to do much with no numbers to go on but a coarser prop will drop the revs and raise the top speed until the revs drop far enough for it not to reach max hp at wide open throttle.

[Mollers]

Hi, welcome. there are 3 or 4 core questions which pop-up very regularly on this site, two of which you are asking. If you use the 'search' facility on the top bar you'll find yourself hours of informative reading on each subject. If you are then unsure fire away with the questions. I hope this doesn't sound too unwelcoming, just trying to save you a little typing.

[Downhilldai]

Originally Posted by jonbmx900

.....it seems to have the original factory prop on it

Why do you think that to be the case?

[jyasaki]

Originally Posted by Mollers

Hi, welcome. there are 3 or 4 core questions which pop-up very regularly on this site, two of which you are asking.

How could he ask 2 questions in one (albeit long) sentence?

jon;

Prop selection is generally done to the emgine mfgr's suggested max rpm, on a boat with a "normal" load (normal is in quotes because everyone's idea of normal is different. For one person, that may be 4 large individuals with dive gear and full fuel, for another it may be 1 110lb person and half a tank.)

This can be difficult (not impossible, just difficult) if the boat has no tachometer. If that is the case, beg or borrow someone's auto tune-up kit, which ideally will have an inductive tachometer.

Selecting the prop comes down to running the thing as fast as it'll go (throttle wide open, and trim up until the prop ventilates, and nudge it back down again), and seeing where the rpm's fall. If it's not in the upper end of the mfgr's suggested rpm range, a prop switch is in order. General rule is 1" pitch equals about 200 rpm; 1/4" diameter equals about 100 rpm. Larger pitch values and larger diameters mean less rpm. Switching from aluminum to stainless should lose about 200 to 250 rpm assuming everything else is the same (it usually isn't.)

4-stroke vs. 2-stroke? I think I'll stay out of that one.

Luck;

jky