Jack plate height

joshgar8

Seaman
Joined
Aug 6, 2012
Messages
65
Alright guys, I know it's not exactly a prop question but props are the closest category I could find. I need help with my jackplate setup. I have searched the forum and came up with how to initially setup a plate. Sounds simple if you have a water pressure gauge..... I do not! I want to play it safe and supply my engine with the cooling it needs but I also want to get the boat where it doesn't spray water on the starboard side of the cowling and porpoise like crazy at cruise speed. I had the engine really low in the water (too low I think) it would porpoise like crazy at 35-40 mph but fast speeds 60-65 it would smooth out. It would also spray water up on itself at any speed on the starboard side of the cowling. I lifted the jackplate up 1" bringing the centerline of the prop shaft 4.375" below the straight edge brought off the plane of the pad. This is a 2.5 mercury 200hp without a low water pickup turning a 25p laser II on a 18ft Astro fish and ski. As far as rpm's go, I already need more prop. With the motor dumped it still redlines before I get wide open without it trimmed out any. Am I closer to where I need to be? Thoughts, opinions, concerns? Thanks allot guys!
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
How about posting nice pics of your current set up to have an overall idea of current jack plate installation.

Happy Boating
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Near as I can tell the boat is rated for 125 hp. If that is right your 200 may be the cause for porpoising.
Pretty sure the hull is designed to go fast so may not be happy cruising as well.
Do you trim down for cruising? Have you tried putting your mother in law in the bow?
Can you look over the back see where the spray starts?
 

joshgar8

Seaman
Joined
Aug 6, 2012
Messages
65
Steele, that's a grand idea about the mother in law on the bow, luckily I don't have a mother in law to go with the mother in law boat. Maybe I should just put 400 pounds of ballast in the bow, I'll take that any day over a mother in law!

In all seriousness, the hull is rated for 150hp. Even if it was rated for 125hp, when it starts proposing, it's not putting out near the 200hp. I am at work now but will attempt to post some pictures of the setup in the morning. I always from in to try and control the bow from moving, that doesn't help at 30-35 mph.

It looks as if the spray could be coming from my transducers however it didn't spray with my 150 before upgrading to the 200.

Thanks for the replies guys.
 

joshgar8

Seaman
Joined
Aug 6, 2012
Messages
65
I did add the jack plate when I changed motors. I should also say that it is a 6" setback just to clarify. Thanks guys!
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
That 200 HP surely is way more heavier than a 150 and sitting 6" further back on a jack plate could make things worst.

Happy Boating
 

joshgar8

Seaman
Joined
Aug 6, 2012
Messages
65
According to the NADA engine guide, the 150 clocks in at 404lbs and the 200hp at 395lbs. I don't really understand that! Maybe it's not heavy enough in the rear. I could make the mother in law ride upfront on the pedestal seat and stash her 9 pound purse in the rear hatch! 😁👍 I think I would rather deal with the porpoising!
 

joshgar8

Seaman
Joined
Aug 6, 2012
Messages
65
No Title

I think it's either the prop or jackplate height or a combo of both giving me issues. Here is a photo I found on my phone. It is not really what we need to see exactly but the best I can do until tomorrow evening.
 

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steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
You have moved 400 lbs farther back and you have a hull designed to run over 50 maybe even 60 you can't expect it to be tame through the whole speed spectrum. You need to move some weight around or tabs or the right prop.A prop that works at 50 isn't likely to work as well at 30.
 
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