1st Boat info

[davis7210]

Hello all. Just found this site and already need some advice! Last spring i bought my first boat. It is a 1983 Hydra-Sport X-260, with a 1983 johnson 90hp seahorse engine. It has power tilt and trim, the prop is 12 3/4 by 21, with a hydrofoil installed. The higest rpm it ran was around 4500 at 42 mph measured by that thing on back with a clear hose attached to speddo. Just reading thru some of the forums it seems that in order for my motor to run at peak performance i may need to install a new prop. Not neccesarally looking for more speed, just optimum thru all rpm range.Thanks for all replys!

 

[SpinnerBait_Nut]

Re: 1st Boat info

Welcome to iboats.
I do hope you have taken a boating safety course.
If not I would strongly suggest it.
Welcome to the world of boating.

You will find the speedos on most boats are off quite a bit.
Best thing is to get a GPS for true speed.
A handheld one does just fine for this,

 

[steelespike]

Re: 1st Boat info

While those speedos are inaccurate it seems your speed is about right.
first thing you might want to do is verify the tach is accurate.You may be able to borrow a tach to check.
Based on a little research setups similar to yours are running 15 and 17 in. props. If the tach checks you may need to get the rpm up.
It would appear you need to drop to about a 17" prop.
that would give you about 800 rpm.should put you at about 5,300.You should check that your motor has good compression and is in proper tune.Check your setup.Especially the height.The anti vent plate(just above the prop) should be about even with the bottom of the boat.You also could raise it until just before venting becomes a problem.Be sure it continues to pump water.You won't make up your rpm but could pick up a couple of mph and rpm.You most likely need that prop.

 

[davis7210]

Re: 1st Boat info

OK, i can check the compression and motor height tomorrow, but not sure about borrowing tach. Will any tach work ie auto tach? As far as prop size is it the 12 3/4 or the 21 that needs to change? also current prop is alluminum, will most likley stay with same. Have not taken boat saftey class ,but very good idea. Only got to run on lake a couple of times last year, most at lake with idle only laws. Hope to do some local fishin tourneys this year,so need to get familiar with water laws! Thanks

 

[davis7210]

Re: 1st Boat info

ok checked motor height, looks pretty close to where it should be.will check compression tomorrow. hope to put boat in water soon,lake levels coming back up. this will give me a chance to see if tach is right

 

[steelespike]

Re: 1st Boat info

OK, i can check the compression and motor height tomorrow, but not sure about borrowing tach. Will any tach work ie auto tach? As far as prop size is it the 12 3/4 or the 21 that needs to change? also current prop is alluminum, will most likley stay with same. Have not taken boat saftey class ,but very good idea. Only got to run on lake a couple of times last year, most at lake with idle only laws. Hope to do some local fishin tourneys this year,so need to get familiar with water laws! Thanks

!2 3/4 is the diameter 21 is the pitch.Pitch is the main concern in propeller sellection.Each inch pitch change gives about 200 rpm reduced number raises rpm.Usually diameter is simply a product of prop design.Main concern in diameter is clearance to turn.If a prop is selected to fit your motor diameter should fit.

 

[davis7210]

Re: 1st Boat info

so looking at prop selection chart,i have the option of 13 1/4 x 17 3 blade or 12 3/4 x17 4 blade. whats best for all around use, again not looking to break speed records just keep motor around for a long time!

 

[steelespike]

Re: 1st Boat info

Go with the 3 blade.Generally a 4 blade is used to solve low end performance problems.3 blade is generally best for all around performance.While your not concerned with top end speed the 4 blade will usually be slower than a 3 blade of the same pitch.The 17 will give vastly improved hole shot and ability to push a full load and the motor should be operating within its rpm range.

 

[davis7210]

Re: 1st Boat info

OK, so i have bid on a prop on ebay. If all goes well should have it by the end of the week. it's a 3 blade 17 pitch .

 

[sc_shane]

Re: 1st Boat info

Hey Davis7210. Welcome to iboats!

I suggest you check this out - http://www.boat-ed.com/ga/index.htm (for those of you that aren't in GA, most other states are offered the same way - I did the SC one here)

Even if you don't spend the $20 for the official certificate, you can learn a lot from the site and get your berrings straight!

You've found the best spot on the web for help solving nearly any problem you can encounter with your boat! There are some true professionals here! Best of luck with the prop!

Oh, another piece of sound advice is to pick up a manual on your motor. You can find a Seloc on eBay for cheap, which is a good start. (some guys say Seloc isn't as technical, which I agree, but it's great place to start for general this and that on your motor) If you start getting into anything hefty, I can't recommend the original manufacturer's tech book enough! Take care!