Prop Question

[broken_line]

thats hoorible my 20 foot tooner gets 16 with just me thats wtiha 28 horse! something is diffenatly worng here. heck even my 5hp could out run you... that prop doesnt look to bad.. where does the cavatation plate sit when the motor is trimmed all the way down??

[boatfixer]

Dont get a prop with more pitch, that will make your problem worse. You are lugging the engine down enough already if you say it has no hole shot or has trouble getting on plane.

To be sure of things, have you checked compression? Make sure your throttle plates are opening all the way, as was already mentioned.

[Northlander]

Dont go more and dont get a "Fin" in most cases they are a band aid for poorly propped or underpowered boats.

[justinman]

.. where does the cavatation plate sit when the motor is trimmed all the way down??

Not sure what a cavatation plate is?

[justinman]

Dont get a prop with more pitch, that will make your problem worse. You are lugging the engine down enough already if you say it has no hole shot or has trouble getting on plane.

To be sure of things, have you checked compression? Make sure your throttle plates are opening all the way, as was already mentioned.

He checked the compression and said it was good. I'll look at the throttle plates... I'll post my findings.

[broken_line]

the cavatation plate is the rectangle flat peice above the prop if that sits below the water it will take a cunk of speed from you cuz it will be hard to get on plane..

[boatfixer]

Not sure what a cavatation plate is?

Its the flat "fin" that is part of the lower gear housing just above the prop. Anti-ventilation plate

[justinman]

So if the cavitation plate is to low it will slow me down? How far below the hull should it be?

By the way I just got off the phone with my tech. He said he checked the throttle & we are getting the carb wide open, so that cannot be it. He's going to get out on the water with me next Monday & he said he can try hooking some timer thing up to some part of the motor...way over my head? I'll keep you posted.

[broken_line]

the cavtiation plate helps push the boat up on plane which makes the boat easier to push making it go faster.. it should be even with the bottom of the hull +/- 1/4" have you tried shifting the wight??

[justinman]

the cavtiation plate helps push the boat up on plane which makes the boat easier to push making it go faster.. it should be even with the bottom of the hull +/- 1/4" have you tried shifting the wight??

The plate apears to be about 1" below the bottom of the boat.

[broken_line]

maby thats your planing problem.. can you move it up 1" possibly?? the more even the better..

[justinman]

maby thats your planing problem.. can you move it up 1" possibly?? the more even the better..

Hey Broken, thanks for the suggestion! Can you tell from the first picture I posted on how to move the motor up. I've read on other post that people move the motors up by one or two holes???? What are they talking about? You're not talking about shifting the whole motor up on the transom are you? I would think you'd want the motor clamps hanging and biting into as much of the transom as possible.

[chickeywing]

Couple more questions:

What brand spark plugs are in there? I've had terrible performance with Champion plugs.

In the first picture, what's the white steel and cylinder? Trim/tilt? Is that a 2nd cylinder on the other side? Is there an oil tank for the system in the back? That's quite a bit of weight in the back.

Does the white steel hang below the bottom of the boat? That could be a huge problem.

[justinman]

I believe I have NGK plugs in there. My marine shop said I was getting a good spark. The white steel and (2) cylinders are yes, my tilt / trim. She doesn't hang below the boat. There is a small hydraulic tank for it, nothing that weighs alot. Other than that tilt/trim system I don't think I'd have any more weight in the rear of the boat that anyone else with a similar boat (battery, gas tank, anchor etc.)

[broken_line]

you can move it up by doing this.. expept use stronger materials.. this is really the only way to do it witha clamp on motor..also make sure there is a safety chain if you cant bolt it on.. i got 6 mph more just by doing this it went from 8 to 14.. trolling motor, me 230 lbs, battery anchor, front casting deck, all my tackle and bait bucket this is ona 13' boat with 5hp

[marine_man]

Cabelas has a something that would do this... I can't recall the name right now, but it's made of aluminum and bolts to the transom and raises the motor mount location.

marine_man

[broken_line]

yeah and it is supposed to make the boat handle better because it sets the motor 5" back or something to... your trim might not work with this on but it will go a little faster with out =)..

[swamptiger]

I have a 25 hp Johnson mounted on a Princecraft Starfish 15. This boat is actually quite fast - I've never clocked it, but it gets up on plane and moves out pretty well with 2 people in it.

But after reading through this thread, I noticed the cavitation plate is actually a couple of inches below the bottom of the boat. I'm thinking of temporarily adding a 2" piece of wood to the top of the transom just to see how much difference it would make..

[broken_line]

make sure you screw the wood to your boat and use safety chains!!!!!

[justinman]

So on Monday I took the boat out on the lake with the shop I've been working with. We checked everything he could think of. Compression and spark were good in both cylinders, no fuel issues, no air leaks. He hooked his timing light up to it and turns out I'm only getting 3100 rpm at WOT. He didn't have any idea why it was so low or how to fix that. He told me with my new prop I should be getting 5500 rpm. I believe we were the same diameter but went to an 11 pitch vs. 11 7/8. Does anyone know what I need to do to increase the RPM? It just sucks to dump $530 into this without getting my performance issues resolved.

[marine_man]

Were you able to get on plane? If so, I doubt you were only turning 3100 rpm with two guys in your boat.

marine_man

[justinman]

No, we couldn't get on plane. We shifted as much weight to the front and still no plane. 3100 is what his timing thing was telling him???

[marine_man]

Ok, based on that now I believe it.

Two questions here...

1) How is it that the shop you're working with doesn't have any ideas? Isn't that what you're paying them for?

2) You could try a 9 pitch prop, but it sure seems like there's something else going on here.. with the rig you describe and the motor hp and prop pitch you should be able to exceed 3100 by a long shot.

marine_man

[justinman]

Thats what I thought I was paying him for too! I wasn't going keep wasting $100 per hour on him trying to figure it out. I paid him 3 hours labor to clean the carburator, install new impeller, check the compression, spark etc, 2 lake charges, new prop etc.

Let me ask you this... I saw the reading on the timer and it read 6200. He said you need to divide that by 2 because of the 2 cylinders. Is he correct?

I'd like to try a 9 pitch but I think the wife will be a little PO'd if I dump another $100 and it doesn't produce any results. I'm even a little gun shy now. Can you return props or is it once you install them they are yours.

Is less pitch the only way to up the rpm's?

[chickeywing]

You should be able to return or exchange the prop. 2 degrees won't make up for 1500 rpm's.

Pull every serial number/part number you can find off the motor/carb/coils/etc...and do some research. You might have some wrong parts.

Did you guys run it with the cover off?