prop selection

[Fish mojo]

1991 4.3 alpha one, 19' spectrum alum v hull. I have a 23P hi-5. run 4400rpm at 38mph. Is this the right prop? At idle speed in gear it does this weird back and forth directional change- let go of wheel and it turns to port for 20 feet, then corrects and goes tostrbd for 20 feet,over and over in a S pattern. Drives me crazy. Any prop suggestions or help for the S pattern thing?

 

[tommays]

Re: prop selection

you will only really no about the prop with trail and error but your WOT should be closer to 4800 RPM<br /><br />IMHP its better to be a littel small than to big which is very hard on the motor<br /><br />the 23 in pitch sounds very big for a 4.3<br /><br />if theres no slop in your sterring you may be over correcting its pretty normal for outdrive boats to wander around at low speeds<br /><br />you have to make small corrections and give time for them to happen<br /><br /> http://www.mercurymarine.com/everything_you_need_to_know_about_propellers5 <br /><br />tommays

 

[jimmbo]

Re: prop selection

Wandering at low speeds like you describe seems to be almost the rule for sterndrives. I know mine can't make up its mind whether to go to port or starboard. As for your WOT rpm range, this has changed over the years. Older engines quite often had WOT rpm of 4200 - 4600. Newer engines are usually 4400 to 4800 with some EFI models now hitting 5000. So check your owners manual and if you don't have it call a dealer and ask for the info specific to that year and model. Depending on what gear ratio the outdrive has, a 23in prop might or might not be too big or too small.

 

[Northern Eclipse]

Re: prop selection

Like others have stated bow steer or wander is typical of a V hull at no wake speeds, Your pitch might be tad to much also 5 blade props will rob top end speed and are usually found to be used on large V6 outboards, If you can "borrow" a small assortment of props you may want to try a 3blade 21p SS 3 blade 23p SS or a 22p 4 blade, I Tried a 5 blade 19p just for my better interest on My 20ft Wellcraft with 350 mag Alpha1, The only thing that it was good for was going in reverse and a rocket launching holeshot but top end suffered a 4 blade gave me almost the same results I still prefer my 3blade 21p Mirage. You just have to experiment a little.