12 foot Sundance

[Fishzilla]

Hello everyone. I own a 12 foot sundance with a 20hp 4stroke Tohatsu. The engine starts and runs great. The problem I'm having is that I cannot plane out the boat. I recently added a jack plate as the engine was determined to be of the wrong shaft length for the transom height. It helped with maneuverability and minor speed increase, but the boat still is very sluggish and doesn't get on plane. The prop is a 9.25" with a 10pitch. Any advice?

Thanks!

 

[tazrig]

Re: 12 foot Sundance

:welcome: Fishzilla. Have you tried putting more weight up front? When was the last time it had a tune up?

 

[MikDee]

Re: 12 foot Sundance

Hey, are you sure your engine is high enough out of the water? The cavitation plate should be flush, or a little above the bottom of the transom. The prop sounds like it's a bit too small in diameter, is this a 2 blade prop, or 3 blade? On small boats like this, sometimes you have to help it get on plane, how is your weight situated? It's not back heavy is it? Can you move some weight to the front to help it plane? I used to have to move as far to the front as I could on my 8' hydroplane with an old 18hp Johnson to get it on plane.

 

[Fishzilla]

Re: 12 foot Sundance

@Taz - the engine is tuned and runs very well. Thanks for the welcome!

@Mikdee - the prop is an aluminum 3 blade recommended by the manufacturer. It's 9.25" in diameter with a 10" pitch. I have a 10" x 7P I can swap out but am afraid to over-rev. The fuel cell is in the bow. My son sits towards the middle and I drive by tiller at the back. The motor is set 4" back from the transom thanks to the new jack plate. The cav plate is an inch above the bottom of the hull when tilted all the way down (electric tilt).

As an update - I just removed the large planing plate that was on the motor. A suggestion from a friend with a similar problem solved. His transom was actually being forced downward because of the delfino.

Thanks for the help gentlemen!

 

[Sea Rider]

Re: 12 foot Sundance

Tohatsu engines likes : (1) to be seated at transom's height for water flow to skim just under small upper water deflector plate, (2) engine riding at 90? when boat's on plane, well ballanced and on flat calm waters. You need to install a induction tach go for a wot spin, but with 2 mentioned points worked out, check max achieved wot with you alone and compare readings against wot parameters factory stated for that engine.

That engine runs happily between 5400-6100 rpm at wot, check rpm achieved with currentt prop, then play with prop pitches all you want to maximize your top wot rpm.

This video can help to match Tohatsu's sweet tranom/engine height match to your combo

Tohatsu 20hp w/ 3/4" shim and proper trim - YouTube


Happy Boating

 

[MikDee]

Re: 12 foot Sundance

@Taz - the engine is tuned and runs very well. Thanks for the welcome!

@Mikdee - the prop is an aluminum 3 blade recommended by the manufacturer. It's 9.25" in diameter with a 10" pitch. I have a 10" x 7P I can swap out but am afraid to over-rev. The fuel cell is in the bow. My son sits towards the middle and I drive by tiller at the back. The motor is set 4" back from the transom thanks to the new jack plate. The cav plate is an inch above the bottom of the hull when tilted all the way down (electric tilt).

Thanks for the info, it all sounds about right. I don't know if running the motor 1" above the cav. plate makes a difference or not, but yes the trim must be all the way down to ninety degrees when starting to plane. Is it better with the fins off the motor, or haven't you tried it since you raised the motor? Usually fins help? Have you noticed any prop blowout at times? If not then your prop is adequate. Getting back to the original problem, how does the boat react when you try to plane out, does it just ride bow high?

As an update - I just removed the large planing plate that was on the motor. A suggestion from a friend with a similar problem solved. His transom was actually being forced downward because of the delfino.

Thanks for the help gentlemen!

 

[Fishzilla]

Re: 12 foot Sundance

I haven't tested it without the delfino yet. With everything else mentioned, it feels as if its about to plane and then the bow rises and the engine just revs with no increase in speed. She really seems like she's about to plane and then nothing. At least it's a little better with the jack plate. I'll report back about the delfino removal when I finally take it out next weekend.

@searider - I'll check that video. Thank you!

Thanks again everyone for all the advice!

 

[MikDee]

Re: 12 foot Sundance

Do you have another prop to try? Now it sounds like your prop is slipping on the internal rubber hub. This occassionly happens, and you can get your prop re-hubbed reasonably, but a new prop, if it's the right one, is not much more.

This is not prop "blowout", a prop will come off plane in a turn, or just randomly at times, if it is too small.

Try the 10"X7" prop, just don't run it at WOT (wide open throttle).

 

[Mi duckdown]

Re: 12 foot Sundance

I think, GOOD Pics of you set up is needed.

 

[Frank Acampora]

Re: 12 foot Sundance

It is a question of weight and balance. Plus, although the engine is good and on a small boat, it is actually underpowered for the load and hull design. I have a little 10 foot racer that does the same thing--bow rises as if she wants to plane then the engine revs up. The engine is mounted about 1 inch too high and until she planed I get over revving. Lower the engine until the anti-ventilation plate is even with the hull bottom and shift weight forward to plane.

If you want to see mine in action go to youtube Frank Acampora videos and search for (I think) Mini Boat Chrysler 60. With a different engine set lower, the problem disappeared.

 

[Fishzilla]

Re: 12 foot Sundance

@duckdown - I will try to upload some pics later.

@ Frank- I feel it may be a combination of many things also.... Weight, balance, etc. i am going to try to move more weight forward.

The engine is actually 5hp more than it's rated from factory. When I got it, the engine was about 3" too low on the transom. The cavitation plate sat 3" below the hull. The boat did about 4.3mph with all kinds of water shooting over the transom. The boat looked like a door stop being pushed through the water. The jack plate now placed it in the correct place on the transom since it is now setback 4" off the transom, the inch above the bottom of the hull is equivalent to being even with the bottom while mounted directly on the transom. It does about 7.4mph now with the bow a bit lower and it feels as if its almost about to go on plane. The prop is just the next thing I"ll be trying.

Thanks for your time and help. It's much appreciated!