Another porpoising thread

[elwopo]

Started a new one instead of dumping on someone else's....

I believe I read that porpoising can occur when the motor is trimmed out too far...and to fix it...trim it in some.

If this is true then I have a question about what happened to me recently.

River boating but pretty choppy as the wind was kicking 15-20 probably.
Started with the motors trimmed all the way in. Hit the throttle full open. Took a while to get on plane and when it did.....immediately began porpoising like CRAZY. Each upward movement higher than the last. Tried it several times in different directions to see if wind or wave direction were a factor. Nope. Did it every time.
Finally just gave up and came in slow and deep in the water (not on plane)

Info:
25' SportCraft Walkaround, twin 200 mercs mounted on platform (not transom), boat has trim tabs (helm adjustable), 60 gallons of fuel in 170 gallon tank.
I don't know the position of the trim tabs as it was my first trip in the boat and have never had them before. When porpoising occured I did push them toward the "bow down" position but it didn't help much.

So if you porpoise when the motors are trimmed out....what could have made this happen?
Want to avoid it in the future.....forever.....

 

[QC]

Re: Another porpoising thread

Popoising is really about weight balance. Too much in the stern. Did this boat come new with the transom brackets? The motors may be too far aft and could cause this although I think she could be fixed/adjusted/modified to compensate.

Trim tabs and trim can/should both help control it, but it is balance that is the primary cause. With that said, what you describe sounds very violent and I would be surprised if you were all the way trimmed in and had the tabs bow down. Both should've helped . . . Have you been out since? What's the position of the fuel tank(s)?

 

[QC]

Re: Another porpoising thread

I did some checking and many of these were built with single OBs although it does look like it was available with twins too. May be onto something, but again they were available. Also, it looks like they have always used transom brackets. Anything else loaded up in the stern? People, Ice chests, concrete ???

That was/is the 251 which is now the 261? Seems like very similar specs for fuel etc.

 

[tashasdaddy]

Re: Another porpoising thread

what type sportcraft, center console, cuddy, sure sounds like you are stern heavy.

 

[steelespike]

Re: Another porpoising thread

From your description I have to wonder if you trimmed in the wrong direction
the slow planing,and imeadiate out of control porpoising sure suggests an error of some sort.Perhaps one of the motors was trimmed wrong do to
some sort of component failure.(trim gauge?)

 

[QC]

Re: Another porpoising thread

It's a walkaround td, it's in his first post . . . I agree with steelespike, but he was pretty adamant that things were right.

 

[fishmen111]

Re: Another porpoising thread

Took a while to plane with 400hp in a 25' WA running 700 lbs. shy on fuel? When you state fully trimmed in, you are referring to the prop(s) being moved towards the bow...right? And you are not moving it until on plane, correct? If so, sure sounds like you were running stern heavy to me. $.02.

 

[Boatist]

Re: Another porpoising thread

I guess a few questions may help us help you.
In general was the bow of the boat too high or too Low?
When on plane where did the spray come off the hull?

Helm adjustable tabs. First make sure they are working.

Two common type control.
Single Joy stick - With this type it just like flying an airplane. You push the stick in the direction you want to be lower. If you want the bow lower you push it straight up. Go a little bit at a time. If you want the bow higher or stern lower you push the stick down. I would start out your first time with the tabs all the way up so push stick down for at least a minute.
Get up on plane if bow is too high push stick straight up and little at a time. if boat is not riding level like starboard high port low then push the stick at a 45 degree angle up and to the right. another way would be to relate it to a clock and to lower the starboard side would push to a position between the 1 and 2 again a little at a time until you get the hang of it.

If you have dual rocker switches then to take the tabs all the way up push the bottom of both switches for 30 seconds to 1 minute. Once on plane to lower the bow you would push the top of both switches. To lower starboard side push the top of the starboard switch. To lower the port side push the top of the port switch. To raise either side push the bottom of the switch on that side. To raise the bow push the bottom of both switches. To lower the bow push the top of both switches.

Your motors trim to lower the bow them trim both motors in. To raise the bow trim both motors out.

 

[QC]

Re: Another porpoising thread

To lower starboard side push the top of the starboard switch. To lower the port side push the top of the port switch. To raise either side push the bottom of the switch on that side.

Boatist has done a great job here, but just to clarify, since just these two sentences might confuse, again, he is describing the bow action as related to the tabs. If you were to watch the tabs they would actually operate just the opposite to the above. Starboard switch operates port tab, up on the switch is down on the tab, thus forcing the Starboard bow down . . . The motor trim is actually the opposite . . . up on the starboard switch, the starboard motor goes up (out), the bow goes up . . .

Bennett Owners Manual