Bow of Aluminum Starcraft hopping at WOT.

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Id would not run a 4 blad
e it will only lift the stern further

Really? Okay well I'd like to hear what D Hadley has to say. When I keep this motor at a 90degree trim, I feel like we are going to fly away!!

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

All that is going on is your prop engine hull combo are at there best.

What exactly do you mean by this?

 

[Tail_Gunner]

Re: Bow of Aluminum Starcraft hopping at WOT.

What exactly do you mean by this?

Generally speeaking most boats launch with there motors tucked in to prevent bow rise or the stern being sucked down.....as they climb on plane or on get plane they trim the drive out..that lifts the bow allowing the boat to run on the stern area....less wetted surface more speed..and a rougher ride of course...Now your boat...its sitting on its tail and gunning down the river lake or whatever.... the porpising your experienceing is the hull finding a spot to rest on then falls off only to lift back up and fall again...very annoying but if your engine is operating at the proper rpm at wide open throttle then the combo has peaked. Like a rock skipping across the water.

Question on a hard launch does the bow pop way up and it takes a while for the boat to plane??? If so your motor is to high...You might have a short shaft engine that needs a long shaft.. or vice versa.That is possible

Take a picture of your boat with the motor running straight vertical with the transom it looks life your runng a bit deep. They will want to see how far the prop is under the keel and were the cavitation plate is in relationship to the keel.


Your running a 16' alum boat...what 600lbs with a 65hp engine??? Sounds fun... but i dont think its rated for 90........

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Your running a 16' alum boat...what 600lbs with a 65hp engine??? Sounds fun... but i dont think its rated for 90........

Hahaha, gotcha. You're right on the money brotha, 610lbs. from the factory. Trust me the coast guard plate is the original, and it says 90hp. The motor is a longshaft, and she gets right on plane. Planes out about 1/3 throttle actually. Cavitation plate is just a smidge higher than the bottom of the boat. If I run the motor with just one other person, and go to 3/4 throttle(or a little less), the porpoising begins. If I run it with 4 people, this thing hauls and doesnt even think about skipping(When trimmed at 90 degrees). And I have run it on glass, and still had some serious skipping. (But when I trim the motor the way it is in the picture, I have no issues with porpoising)

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

And when you say the combo has peaked, do you mean that it is taking the most power that I can throw at it?

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

If your prop is indeed 11" diameter it is over 2" under sized for a 17" pitch this could
make it harder to control the boat with trim.Going to a 4 blade may be premature and a
good 17" prop may solve things.A proper sized 17" may reduce rpm as a 2" diameter increase
is signifigant.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

If your prop is indeed 11" diameter it is over 2" under sized for a 17" pitch this could
make it harder to control the boat with trim.Going to a 4 blade may be premature and a
good 17" prop may solve things.A proper sized 17" may reduce rpm as a 2" diameter increase
is signifigant.

Okay gotcha. So as a rule of thumb, and increase of diameter in 1" should change my RPMs by how much?

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

As near as I can tell the 650 calls for about a 13" diameter.With that severe difference there may be a reduction in rpm.
But your 11"X 17" prop intended for your motor would be an exception. To me it's all most like someone took a prop intended for a smaller motor and put your hub in it. Does it appear a 13" prop would fit on your motor?

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Does it appear a 13" prop would fit on your motor?

Yes a 13 would fit. I think this motor came stock with a 13" X 16P prop.

 

[sschefer]

Re: Bow of Aluminum Starcraft hopping at WOT.

It's those two batteries and the fuel up front. Stick them in the back and give the motor a better chance at holding the bow up. A whale tale or smart tabs would then be effective as stern lifts and help in getting up on plane with the extra weight in the back.

I should proably qualify this with "I made the same mistake with the batteries".

Added... My 60 4 stroke runs a 12x22 on a 1:1.83 lower. Thats stock if that helps for reference.

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

WOW! a 12 X 22 on a 1.83 lower sounds way out of line unless your boat weighs about 8 lbs and has a very fast bottom.

 

[Tail_Gunner]

Re: Bow of Aluminum Starcraft hopping at WOT.

WOW! a 12 X 22 on a 1.83 lower sounds way out of line unless your boat weighs about 8 lbs and has a very fast bottom.

Well that boat hull is a flat bottom.... 600lbs...65 horse. Actually a 20 horse motor would plane it out. Id be willing to bet it's running on the cav plate at wot.....

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Well that boat hull is a flat bottom.... 600lbs...65 horse. Actually a 20 horse motor would plane it out. Id be willing to bet it's running on the cav plate at wot.....

Well it does have a slight V in it. Actually when I was by myself on it and used my 9.9hp when the main motor was acting up it planed me out! As hard as that is to believe.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Alright fellas, thanks for all the input. So here is what happened this weekend. I had my dad on board and we headed out. I have a bit more weight in the front now as I have added the fishing platform up there. I had a 6 gallons more gas under the console. I trimmed the motor up two holes from the bottom, and the porpoising happened a lot later in the RPM range. I put a tiny tach on, and got great readings up to 1500RPMs and then from 1800RPMs and higher it still read 1800, but that is another issue. I TRIED to get some RPM readings, but didnt happen yet. Anyways I had my dad move up front and sit on the platform, and we did not porpoise at all. speed at WOT was 32MPH, and cruising speed was 25MPH. According to the prop slip calculator, with a 2.3:1 lower unit, 17P prop, and about 10% prop slip the motor is pegged at 5200RPMs, which is right where we want to be. I will try and get another reading from the tinytach this weekend, but as far as I can tell, I am expecting that I want to switch to a 16P 13" Diameter prop, or maybe even a 17P 13". What do you guys think?

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

If that is a 4 cylinder I think it requires special shielding to avoid stray pulses.
You could try going from the bottom plug and run the wire outside the cover as soon as possible.
also don't use any knots in wrapping the wire.
I think you will have more choices in a 17" prop.
It is possible the 2" difference in diameter could reduce rpm a little difficult to estimate.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Cool thanks Steele. I did run it to the bottom plug, I was thinking about putting a bunch of shrink wrap around the wire. I told the factory that sent it to me to shield it, so they did. I have some excess wire wrapped into a zip tie, could that be causing issues? And you are correct, I dont think there are many 16P props to choose from for this motor.