88 Predictor rigging

[SpikeJ]

I have read several threads on boat rigging and I am still confused. I read about prop shaft height and and unsure what is the best starting place. From what I am gathering the higher the better (water pick up aside), but my impression is that it will effect the time to plane and might make it harder to plane with skiers? Secondly it would seem bigger prop diameter would give you more bite and more pitch would give you more speed as a basic starting point. Is that correct?


1988 Predictor 115 Mercury Inline 6

 

[1979checkmate]

my trimate II with an inline 115 likes the propshaft about 5" below "pad". (this is with 6" setback). its still deep enough to take off very, very well, and lets teh motor rev out better. at this height i also do not have to worry about water pressure

 

[SpikeJ]

Thanks. I am starting to get a better picture. My prop centerline is 6" below the "Pad". right now I have an old beat up prop with the numbers 48 32744A4 21P the pitch I am assuming is 21 Looks like a Merc # 32744A4 but I can't find any info. Anyway I use this for ski & tubing because it seems to get up out of the water best but no good for speed, top speed with this prop is always at the top end of my recomended WOT 6000 rpm. The boat came with a Quicksilver Stainless Steel 48 75768A5 20P but it was tough to get it up out of the water quick for skiing or tubing. The long and short of it all is that I am repalcing my lower unit and I could lower my engine 1 more bolt hole and I am wondering if this would get me up out of the water better with the Quicksilver Stainless steel prop. The pitch only changes 1" so I would think only a little change in RPM's. The design of the 2 props is significantly different, so I would say their is more to the performance than simple pitch changes. Lastly when tubing and turning corners I sometimes lose all my grip with the 20P prop, ventilating the prop??? Looking for any suggestions while we use it for tubing & skiing a lot who doesn't want to faster when you can!!!

 

[john lamon]

lowering it won't help your hole shot any, if I'm pulling up a real heavy guy I put my jackplate as high as it will go and then lower it once on plane, if you think about for a second it makes sence that the lower the prop is on the transom the more the bow will lift.

If you pull skiers all the time and you want a better hole shot your better off looking for a 4 or 5 blade prop, they work great for water sports, most 3 blade props will lose bite in the corners.

 

[SpikeJ]

I don't have jack plates. Maybe down the road. So lower won't help the hole shot. It sounds like you use your jack plates to raise it. Would raising it help? the eailier thread said "its still deep enough to take off very, very well" like making it deeper would be better. I'm not quite sure what is best.