How to stop porpoising???

[BRzuki]

I'm having a terrible time with my boat porpoising. The boat is a 1548 aluminum with 8* V and I am currently running 6" of set-back. I run either a 25hp yamaha 3 cylinder or a 40hp Mercury 3 cylinder. When I first got the boat I set it up with 11" of set back and it porpoised bad. I then moved down to just 6" of set back and it still porpoised very bad. I went with a low rake prop on my mercury and that seemed to help slightly but not anything like I had hoped. The boat porpoises even worse when I add some weight to the front like some have told me to do. I was also told that adding some hook in the outside and next to outside strakes 6-8" from the stern would help to raise the stern and push the bow down letting me trim out and gain speed, however everything I've read is that the bottom needs to be very flat and straight so that contradicts the "hooking" idea.

I'm needing any and all ideas that might work as I'm very disappointed in the performance of the boat as it is now and have two "worked" motors that are not reaching their full potential.

Thanks in advance.

[Cubman]

Hooking the hull worked for me. 1/8" on just the outside strakes was all it took.

[microbream]

I assume you have played around with the trim and weight distribution?
try trimming it in
i have a light boat an experienced the porpoise ride! it can be scary
buy a bigger pitch and drive right though it, i say !!

[chris3298]

I'm having a terrible time with my boat porpoising. The boat is a 1548 aluminum with 8* V and I am currently running 6" of set-back. I run either a 25hp yamaha 3 cylinder or a 40hp Mercury 3 cylinder. When I first got the boat I set it up with 11" of set back and it porpoised bad. I then moved down to just 6" of set back and it still porpoised very bad. I went with a low rake prop on my mercury and that seemed to help slightly but not anything like I had hoped. The boat porpoises even worse when I add some weight to the front like some have told me to do. I was also told that adding some hook in the outside and next to outside strakes 6-8" from the stern would help to raise the stern and push the bow down letting me trim out and gain speed, however everything I've read is that the bottom needs to be very flat and straight so that contradicts the "hooking" idea.

I'm needing any and all ideas that might work as I'm very disappointed in the performance of the boat as it is now and have two "worked" motors that are not reaching their full potential.

Thanks in advance.

Like others who have helped me here with my boat it really is helpful to have a picture of your setup.

I have had problems with porpoise but if you have some trim tabs it will help but the boat needs to be totally flat on bottom. If it has the slightest hook you can forget about trim tabs. This was my experience with a 14 carolina skiff.

Chris

[Fastjeff57]

My 9 footer (70 hp Merc) would do that, so I added trim tabs. I can dail in enough tab to eliminate the porpoising, and remove it for speed runs.

In the photo, an electric cylinder was used to actuate the tabs. Before that, I used a long, threaded rod with a handle on top.

Jeff

[zul8tr]

To get a hull and motor combination beyond the porpoise stage can be achieved by several means some easy amd some more difficult. They are in no order: more hp, engine setback, correct prop, engine trim angle, proper location and amount of hydrodynamic and aerodynamic lift, hull bottom desgn. With your hull aero lift is what it is and not much can be done without significant deck mods. Hydro lift on the bottom is also limited in your case due to the hull you are using. Hull bottom design can be modded somewhat as noted in posts with some hook (not recommended since not adjustable) or trim tabs (preferred and easier to do and adjustable). If $$$ available more hp :D

Once tabs are installed they can be adjusted to suit. Note that ideal would be tabs down enough to control porpoise and prop shaft parallel to bottom. Once achieved then start to raise the engine. Also note the greater the setback usually the greater the chance for porpoise due to increased distance from the pivot point near the rear hull bottom then more down tab is required to compensate. These adjustments can only be done by testing to achieve your goal (???? decide on what this is) for best speed (and/or manuvering) with the least drag. Along the way prop changes may be also in the cards.

A tach and a speedometer is a must as well as good note taking of changes being tested, Do one thing at a time then test., if conditions change note it.

With $$$$ and perserverance :eek:almost anything can usually be achieved :)

[sheuninck]

needs to be 1 beam forward.