22% slippage go up or down with pitch?

[procraftguy]

Go up or down in pitch size with 22% slippage currently 19 pitch on 1976 mercury 1500 inline its running nice in water so up down is good just want a little better speed

 

[steelespike]

We need to know your wot rpm and gps speed also size and weight of the boat.Do you know your gear ratio?
Very often tach reading are inaccurate same for speedometer.

 

[procraftguy]

4900 rpm 34 mph. Gps 1988 1780 v procraft fish and ski 2 ppl in boat calm no wind flat water doing height test inspection rides in water perfict av plate skimming top on plane has more that is not wot but was thinking i should have been around 15the %

 

[Texasmark]

Looks like you used the prop slip calculator. Great. You are way down in rpms and speed. Seems to be the same boat as my son's per the posting yesterday. I'm going to say that your engine isn't putting out 150 ponies with the things you have added herein. Or the boat is severely water logged.

HTH,
Mark

 

[Georgesalmon]

Think that engine is either 5000 or 5200 WOT RPM. If so you should probably drop to a 17 pitch which might get you to 5300 WOT RPM.

 

[procraftguy]

Yes it is texas its not waterlogged i rebuilt here last year all new foam and transom that test was yesterday was checking ride hieght never got to wot that was involved lol and never seen more then 3/4 throttle does that make a diffrence?

 

[procraftguy]

Ps my wife was to scared to go faster on are small 125 acre test lake

 

[steelespike]

Partial throttle reading don't mean much.We need to know what your motor can make at wot.If the motor is healthy you can over rev it briefly to get a wot reading.
What gear ratio are you using.Slip will usually be higher at lower rpm.
My after market service manual indicates 5300-5800 for the 1500.

 

[MikDee]

Ps my wife was to scared to go faster on are small 125 acre test lake

They are all that way! So, what does your girlfriend think? :lol:

 

[Sea Rider]

If you have dilaed on flat calm no wind waters, which is the way to go, for AV plate to skim assume at water level, that setting will work well on flat straight water courses, will probably have axcessive prop ventilation on tight close turns, choppy, windy or wavy conditions. If experiencing so must lower engine tad lower until prop cavitation stops. Make a new sea trial with engine sitting at 90 deg angle on transom and boat riding paralell to water level once on plane and check

Happy Boating

 

[procraftguy]

2:1 ill recheck the wot when wifes not along i just felt at 4900 rpms i should have been around 40 from what iv researched i t sounds like a beast and iv done just about everything i know but prop and im cluless in that department

 

[Texasmark]

Yes it is texas its not waterlogged i rebuilt here last year all new foam and transom that test was yesterday was checking ride hieght never got to wot that was involved lol and never seen more then 3/4 throttle does that make a diffrence?

Absolutely! 125 acre is too small to get the woopie out of that rig. 3/4 throttle would not get the efficiency out of the prop I spent time to recommend to you and in telling you why you wanted what I said.

I'm checking out on this thread. Dead end!

Mark

 

[Bob_VT]

If that is your WOT RPM 4900 then I suspect you are NOT running on all cylinders. Inline motors like to breath and run .......running between 5500-6000 is better. You need to check the motor. An inline will run and rev up in N while missing 5 cylinders and your numbers indicate a dropped cylinder.

 

[steelespike]

He wasn't running at wot due to the very small lake

 

[procraftguy]

Ok so my ignorance on the not being at wot took on larger lake mon & tue while camping and got 5300 rpms 49 mph 2 on boat still not sure if thats all its got but it was there in 25 sec went for 1/2 mile stayed right there

 

[steelespike]

OK ,the numbers don't quite add up.Can't go 49 at 5300.Need speed by gps. Present speed is probably about 41.5 guessing 13% slip.
​ If the tach is original it is suspect.
41.5 with a 1200 lb boat with 2 aboard seems like a good ball park base line speed.

 

[Texasmark]

Ok I lied. I'm back. That's more like it. Where is your trim? Seems to me if you have some trim left, you can push her on out and raise the bow some more and move on up the rpm and mph ladder. With that done I'd say you are there.