Pulse 186 Porpoising; Jackplate & Smart Tab?

[Gdog]

Hello Everyone,

I've read through several threads regarding porpoising on Pulse boats, in my case, a 186 with a Mercruiser 175 Xri mounted to the transom, with a stainless Stelleto 23p x 14" 3 blade prop (10323 m1423). I realize that some or most of what I'm about to ask might have been covered before, but I haven't found the answer yet. It would be really awesome if someone would write a thread called "The definitive guide porpoise elimination on a Pulse," as it seams to be a common problem.

Right now I can do 58 mph @ 5600 RPM with 3/4 tank of gas and 450 pounds of people. That's plenty fast for me. What I'm really after is the elimination of porpoising in the 30-40 mph range. I've considered Smart Tabs, and ultimately may end up with them regardless of whether I buy a jackplate or not. But right now, my cavitation plate is about 2" above the pad, and I've read that it should be at least 3" above, perhaps more. Prop centerline is 6" below the pad. I can trim as high as I want at speed without a blowout. I'm considering a 10" Slidemaster manual jackplate mainly for adjust-ability, with the hope that it may help my porpoising, and the fringe benefit of more speed. Will the jackplate do much for the porpoising? Will simply raising the engine help? I can go up 3 holes right now.

The Pulse jumps out of the hole nicely. But I have considered an aluminum 4 blade prop, perhaps a Nemesis, for drive-train insurance reasons against rocks. I like going fast, but I don't need to wring every last MPH out of the boat. Will a prop like that also help with the porpoising?

Thanks in advance for all of your insights!

Grant

 

[Gdog]

I realize I gave a lot of info and it might have buried the main point of my question. I'm considering buying a 10" jackplate to eliminate porpoising on my Pulse 186. Is there a reasonable hope that this will work? There's a used one local to me now.

Thanks!
Grant

 

[PA-Checkmate]

not much help, but even my convincor will porpoise some until I'm about 40mph. I think it's just the nature of the setup. That said I would purchase the electric/hydraulic plate so you can adjust for low and high speed use. I'm sure others will comment.

 

[KevinR]

I have a friend that fixed the issue (same hull) by placing 60lbs of sand bags in the bow. he has a 225 on 10" hydro plate and runs a Bravo 4 blade. hope this helps

 

[Gdog]

not much help, but even my convincor will porpoise some until I'm about 40mph. I think it's just the nature of the setup. That said I would purchase the electric/hydraulic plate so you can adjust for low and high speed use. I'm sure others will comment.

Thanks. I'm a cheap skate, and I'm ok with a single manual jackplate setting that would probably favor high speed, or else just find a height that helps with the porpoise issue.

I did find one particularly insightful resource on the general subject of porpoising, if anyone's interested:
https://www.screamandfly.com/content.php?325-Porpoising-Why-It-Happens-and-How-To-Fix-It

 

[Gdog]

I have a friend that fixed the issue (same hull) by placing 60lbs of sand bags in the bow. he has a 225 on 10" hydro plate and runs a Bravo 4 blade. hope this helps

Interesting that neither a 4 blade prop nor the jackplate solved the issue for your friend. There is a spot in the tip under the bow cover where sand could sit without even being seen. That might be the simplest fix.

So, I guess the real point of the jackplate would be speed, and looking cool. I've never messed with engine height before. I might try moving up a notch or 2 just to see what the effect is.

Thanks for your help!

Grant

 

[ianz]

The 10” jack plate will make it worse . If you reeallly want a jack plate consider a smaller 5” on. Different prop may help