jackplates and propping

[95glas]

have a 88 hp johnson, thus far have tried 3 different props but haven't found one I am truly happy with... installed a 6" jackplate and am about 1/2 up on it and still have good water pressure ( actually want to go higher) problem I have is all the props I have tried either slip or ventilate ..thought part of the advantage of running a jackplate is for the cleaner water for the prop to bite into? thinking of sending 2 of the ss props I have into a prop shop to get modified...1 of them is a 4 blade which I bought hoping it would allow me to remove the hydrofoil...its better but still porpoises..thoughts and/ or suggestions? thanks

 

[KDAVID1]

Re: jackplates and propping

Do you have electric trim?

 

[SparkieBoat]

Re: jackplates and propping

you raise your motor until prop starts to ventilate...any prop will vent at some point. find a prop that gets you around 5800 RPM at WOT, with motor as high as you can get it with out it venting. trim tabs will stop the porpoising and give you a better hole shot and you could remove your hydrofoil if you want, but it will help stop prop venting, so I would leave it on, if you have your motor jacked up it should be out of the water any way at WOT and trimmed up.

 

[95glas]

Re: jackplates and propping

got a bit more room to play with then.. the 3 blade gets about 5000 rpm and the 4 blade 5500.. thought of getting a surface piercing style prop but doubt anyone makes for a 88. any huge negatives if went that route?

 

[SparkieBoat]

Re: jackplates and propping

no huge negatives, you would be spending your money on the wrong thing though...spend money on trim tabs first, then you will probably not need to do anything to your prop, if anything I would drop 1 pitch on your 4 blade prop. but 5500 is ok.

 

[95glas]

Re: jackplates and propping

any input if a 19 pitch 3 blade ss prop would help? not sure if i am seeking the unobtainable? 45 mph out of a 88hp johnson? bouncing around 40 is my best yet- no point imo going any quicker... max speed on any lake around here and what I have seen all are heavily enforced ..the 4 blade got sent back, just have a unknown pitch 3 blade aluminum and a 17 pitch apollo ss prop - got about 5000 rpm out of that- also have a bobs exhaust housing but haven't got to around yet to testing with it partially/ unrestricted

 

[SparkieBoat]

Re: jackplates and propping

you need to prop your motor to turn 5500-5800 RPMs, ( motor MUST be in proper running condition and properly mounted first ) when it hits that, that is about what your top speed will be. you might test 20 other props and get 1-3 MPH more or less. if a 17 P prop is only turning 5K then you would do WORSE to put a 19P on it. you want your RPMs to go up not down, but with your motor only turning a 17P prop 5K I am wondering whats up, (maybe motor issues) you never mentioned the boat it is on, weight, length, ..if you want to stop the porposing and get a better hole shot ..get trim tabs, raise your motor as high as you can without it venting the prop. then prop to hit 5500-5800 RPM, this will be the best this setup can run for you... If you want to go faster put a 150 on the back.

 

[95glas]

Re: jackplates and propping

was just thinking would be faster with a 19.. even though the 4 blade revved more seem to be slower than the 17- granted 4 blade vs 3 blade... trust me have thought of a bigger motor- capacity plate says only rated for a 130 hp and on the evinrude site for boat tests for 130ish motors on boats similar lengths to mine don't seem to be any faster... probably just get there quicker? was thinking of added a spacer to to see if that would help.... this is probably one area the boat i got rid of ..a 1976 16' sidewinder would be superior to my 1995 glastron gs160

 

[SparkieBoat]

Re: jackplates and propping

a 130 should go much faster than your 88. probably at least 5-8 MPH maybe more. I still am not sure that you are not having engine issues, a 17P prop on a 88HP on a 16' boat should turn over 5K unless the boat is heavy or the hull is rough. a 150/175 2 stroke is the same weight as a 130 in the OMC motors. I am not sure what a spacer is, you already have a 6" jack plate, so I am not sure what you are talking about.

 

[95glas]

Re: jackplates and propping

transom spacer that goes between engine and hull..cheaper than getting another jackplate to try.. but have been told would probably increase my boat's tendency to porpoise.. thought of getting a adjustable composite pitch prop to try but doubt comparing apples to apples as can't really transfer that to a ss prop imo.. just going by what the capacity plate on the boat says.. worried if stopped and officer sees better than capacity plate says screwed...the 17 pitch probably would rev slightly higher but can't trim up any much with it or starts to porpoise.. had trim tabs in my possession once but never installed them as thought would have to eliminate the swim ladder to use them

 

[SparkieBoat]

Re: jackplates and propping

trim tabs should install under a swim ladder, if it is the platform type ladder. the porposing indicates the motor may be still too low, also if you can trim without blowing out. a engine too low will cause drag and under preform, I have covered this 2 times already in this same thread..trim tabs will make a huge big difference well worth making them work even if you have to get another swim platform.. A 130 would go much faster, but you can get better out of what you have, but the Prop is the LAST thing you need to get/do. do everything listed in post #7 and you will get the most you can out of your current set-up and should not even need to buy another prop, that 17 should be good for you. do not forget a motor in proper running condition means you have done a compression, spark, carbs, fuel pump/lines, tune-up and linkage check/repair..o yea, do not use a spacer with your jack plate, if you want more space get a 10" or 12" jack plate..but this is not needed, the one you have should be fine, just use it and jack your motor up till the prop starts venting, then down just enough to make it stop venting.