I have a 1984 glstron boat wit a 70 hp motor with a 13x15 pitch prop. and have to play with the power trm to get boat to plane out. How do I know if I have the right pitch prop.?

Probably not. Check the prop for pitch. Often you need to change the prop depending on the load so the engine can reach proper rpm.

sounds like you have gone to far down please let me know where the lower cavitation plate is in relation to the keel (ie hieght difference

props are available from any boat shop or on e-bay
if you prop problem is a failed rubber insert, they can be replaced by any accredited boat shop
what you need to know is the pitch of the prop as there are at least 3 different pitches depending on what you do with the boat, before you purchase on line

you are dealing with the constant series of compromises between hole shot or top end. Need to know diameter of props, but increasing the diameter by 1/2" on the four blade will help top end, and then try increasing the pitch to maybe a 22 if hole shot is still good and top end lacks. You could also add trim tabs if you don't have them to help you get on a plane faster as well.

Evinrude 50 HP Bogs at WOT - MarineEngine

www.marineengine.com > ... > Johnson Evinrude Outboard Archive

Aug 6, 2002 - 17 posts - ‎3 authors
83 50 HP Evinrude - sat out in weather for 4 yrs. Been cleaning ... At WOT, she bogsdown. Up to. ... Yes, this boat/motor is new to me. Actually ... Mercury 50 1987 bogs down when full @ full throttle
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Check the size and pitch of the prop. By reducing the pitch you will get better hole shot out of the water ,but my be lose a little top end speed. This will be stamped or cast into the prop eg: 15x21 which stands for 15 inch diameter by 21 inches pitch.

Try adding a plane to the lower unit of the outboard motor.
SE Sport 200 Hydrofoil
This will plane out the boat quite well.

NO.What you will have is a boat that has slightly more hp.It's only 3% increase.Your boat will get up and go slightly better but in the end think of this.
4000 rpm is still 4000rpm.The engine is still spinning at the same rate even if it has 400hp.
The cheapest and most effective way to alter things,is with a different prop.Be it a 4 blade ,3 blade,slightly more pitch.Run the boat and see what you get out of it.Then decide what to do.Props are a LOT cheaper than gearboxes.As a unofficial rule,a change of prop pitch by 2inches is going to change the revs by 'about' 500rpm.Eg. 26inch pitch= 5000rpm,24inch pitch=5500rpm. This will vary slightly boat to boat but it's a good starting guide.
Hope this helps you

you could try a lower pitched prop.2" would up the revs by 400 revs.,which would up the revs ,but give you more low down thrust,and/or tucking the motor under more[if you have electric trim/tilt].thats a big boat and fair bit of weight for a 40hp..my 40hp merc is on a 13ft saracen,and with two of us it takes a while to get gooing.so i bought a ProPulse prop,with adjustable pitch.been god to try different pitches

I have 1969 5hp Johnson. Starts and runs good, but will only push a 14ft row boat slow at low to medium rpm. When at higher rpm the the motor just revs up and the boat slows down to almost nothing just like it has seaweed around prop.Any help would be great.