Proper Engine Placement??

[Fish boy]

Can any one give me some advice?? It seems that no matter what I try, I cannot get much more than 50 mph out of my boat. I recently repowered hoping that more HP would help, but despite 230 on the dyno, I cannot get more that 50mph out of this boat. Currently using a Mirage 3 blade 23x14.5 turning 5600 rpms.

Budmann suggested that it might have something to do with my lower-unit being too low. Does anyone have any thoughts regarding the placement or any thing else that might make a difference? My baby looks fast, but right now she is a sheep in wolf's clothing, and I am afraid one of these days a bayliner might call my bluff.

Thanks,
Jody

http://www.donzi.net/photos/jstaples42.jpg
http://www.donzi.net/photos/jstaples43.jpg

[MOP]

You are to low, I would go up to the third hole. Try that, you may loose some hole shot maybe not. There is a 16 here with a 140 JohnRudy on it that is up 2 inches he runs around 50 you will be much faster once you hit the right hieght and prop.

[Jamesbon]

Try a hydraulic jackplate if you don't already have one. I run about 62 with my 200 Merc. jacked up 3.5" from the point where she'll plane out. In other words, if I try to plane off with my engine up 3.5", it will cavitate so much that it won't plane. So I lower it down to the "planing" position (which is 3.5" lower) and get on plane. Once planed off, I start raising to the 3.5 mark. The 3.5" mark only works at speeds above 40-45. (or it woill cavitate)

Here's a pic (http://www.donzi.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=7;t=000039#000000) of my Rabco 19 with 200 on a hyd. jack plate.

How many rpm's are you turning and what length boat? Have you checked for rocker in the bottom?

Just had a brainstorm. I'll shoot a side pic of the engine in full speed height, and then another of it in planing height and we can look at the difference. Check back later tonight...

[riverrat]

I would agree with the other posts. I would look at my set back & a jack plate to start with. I would also find out what the intended hull speed is for your boat. a 50 mph fishing boat is a common #.
my 2 cents.. :D

[Fish boy]

Thanks for the replies. I have a Jackplate-the picture shows all the way down. based on the feedback, I think I should probably adjust the engine height up (before I start jacking it up).

The boat is a 23 foot 1988 Donzi f-23. Cavitation is a big problem, which is one of the reasons I put the spacer plate in to lengthen the shaft in the first place. As far as intended hull speed, I rode in another f-23 with a yamaha 225 that did low 60's. I would be happy with that, but would love more.

Is there any realtionship to the nosecone and the bottom of the hull as to where this should be set?

Is there anything to the suggestion that the foam may be holding H2O therefore making it heavy? Had a little incident with the no name storm while sharkfishing in the gulf or Mexico.

Thanks again for the responses and patients with my stupid questions.

Jody

[Jamesbon]

Can you adjust your jack plate (electronically/hydraulically) on the fly, or is it manaul? I guess the point I'm trying to make is the optimum engine height for max speed will most likely cavitate when attempting to plane off if you have a manual jack plate.

Can you inspect all compartments below decks for trapped water? The foam that surrounded the gas tank in my Donzi was saturated with water.

The first pic shows the skeg in position to plane off, fully down on the jack plate and trimmed all the way in.

The second pic is of the skeg in "balls out speed position." Jacked up about 3" and trimmed up 3 seconds on the trim button. In this position, it's impossible get the boat on plane...hence the hydraulically/electronically adjustable jack plate.

If the lift wasn't in the way, we could take a look at the relationship between the nose cone and keel. I'll take a look in the light tomorrow for a shot of that if possible.

http://www.donzi.net/photos/nscjack1.jpg

http://www.donzi.net/photos/nscjack2.jpg

[Fish boy]

Nathan,
thanks for the pics, that helps a lot. I am definately too low on the transome. I wil try try to eyeball my lower unit with your pics to start and see how she runs. I really appreciate your help.

On a side note, I noticed in the thread with your pic from shell island that you mentioned asking the owner of Rabco a question if you met him. I grew up in StPete/Clearwater and Randy Rabe is a family friend. I have not seen him in several years, but I am sure I can get in touch if you would like to make contact. Please let me know.
Thanks gain,

Jody

[Fish boy]

Riverrat,
I finally figured out what setback is (duh). I do not have much setback. do you have any suggestions? I found a couple brackets that go from a few inches to 12 inches. Are there any drawbacks to changing the setback?

By the way, great avatar!

Fish

[MOP]

Since you already have the jack, what I would do for a starting point would be to trim the engine level to the bottom. Them using a staight edge from the bottom move the engine up 2 inches, you could go higher with more stand off. But 2 inches will be pretty close for what you have.

[Fish boy]

Thanks MOP, I will try that tomorrow and let you know how it worked.