2003 Sea Pro 235 WA Outboard Height...

[chaps]

This conversation started in my thread on the "Sea Pro: Models by Year" thread. I thought I should move the conversation here. A member here noticed the 5" shaft extension on my Yamaha 225, making it 30" long and was surprised to see that on a boat manufactured with a bracket. This member was curious how the boat performed. 

Currently it is propped with a 17P three blade SS prop. Approximate WOT is 5800 RPM and top speed is around 45 MPH (in choppy water) When running the boat out of the hole I have to trim the outboard up about 40-50% of the travel of the trim gauge to make it fully plane out. Otherwise it doesn't climb out very well and I have rooster tails coming up from either side of the out board before it climbs out. I think the rooster tails are coming mostly from the "pontoon" under the bracket. (See the pictures below) There are pics showing the height of anti-cavitation plate in relation to the keel. One pic shows the motor trimmed all the way down and another shows the motor at about 50% of the travel of the trim gauge (roughly parallel with the keel) As for raising or lowering the motor, I can either raise it two holes or lower it one hole. Any toughts?

This is the first boat I have owned with a bracket and an outboard. All my experience is with larger twin stern drive boats. Most recently a Calais Marine CM3000.

[gnrphil]

Hey chaps, sorry for the delayed response but I was on vacation.
My curiosity was sparked because usually when an outboard is set back from the transom (with a jack plate or bracket) the "rule of thumb" is to raise the outboard 1" for every 12" of set back, reason being is that when water leaves the bottom of the boat at the transom it rises therefore the outboard needs to be higher the further back it is. A 5" extension on the outboard has the opposite effect in making the outboard longer thus lowering the foot, now I'm not saying it's wrong by any means it just doesn't make sense with my limited knowledge on the subject.
Thoughts on the planning issue:
If the outboard is in fact too low in the water , it would create a lot now drag which you are trying to overcome to get over the hump. Top speed and RPM's look decent however. Have you tried using some trim tab when planning ?, maybe that would help.

[yessnoo]

Ok I am definitely not an expert on this so take anything I say for a grain of salt. I have a sv2100 with a jackplane on it so it is nothing like your setup or boat style. However I believe the principle would be the same from what I have read. Generally when trying to find the best motor height for any given constant power/trim setting the procedure for using a jack plate would look like this:

1. set throttle and adjust trim for maximum speed and rpm
2. raise jackplate slowly while monitoring for speed and rpm increase.
3. at some point while slowly raising the jackplate the rpm/speed will not increase anymore and a degradation in performance will be noticed (very small)
4. lower jackplate a small amount from the degradation level and that in theory should be the most efficient running height for that power and trim setting.

So if the above theory was correct I would raise the motor one hole and run it. If it runs better then you can decide if it is worth raising another hole. If it does worse then just lower it back down. I have never personally raised or lowered the motor mounted position but from other threads on this forum it doesn't sound like it is very difficult. I guess my point is it sounds like people generally raise the motor until they hit the limit rather than lower motor.

If it were me I would have to raise it just because my curiosity would get the best of me otherwise lol

Also it seems weird that you have to trim up to get out of the hole because generally you should be trimmed all the way down for best hole shot...maybe the bracket does something I am unaware of or the motor is in fact too low causing too much drag as stated above

[chaps]

I have an edit on my top speed… My chart plotter GPS speed was incorrect. I installed a new chart plotter and found that my top speed is about 35-37 mph. I’m thinking I may raise the outboard one hole and see if I get better results.

[gnrphil]

Jun 29, 2022 0:18:25 GMT -6 chaps said:

I have an edit on my top speed… My chart plotter GPS speed was incorrect. I installed a new chart plotter and found that my top speed is about 35-37 mph. I’m thinking I may raise the outboard one hole and see if I get better results.

Are you sure the new chart plotter isn't reading speed in Knots ?, check that first.

[chaps]

Jun 29, 2022 9:33:22 GMT -6 gnrphil said:

Jun 29, 2022 0:18:25 GMT -6 chaps said:

I have an edit on my top speed… My chart plotter GPS speed was incorrect. I installed a new chart plotter and found that my top speed is about 35-37 mph. I’m thinking I may raise the outboard one hole and see if I get better results.

Are you sure the new chart plotter isn't reading speed in Knots ?, check that first.

Already checked that. The older chart plotter was only getting intermittent gps signal and not that this matters but also did not have a chart card for the area I was in. The newer one that displayed 35-37 mph has solid gps signal and has a chart card for my area. I am certain that is my top speed.