Porposing - 2900 SCR

[martyc]

Just bought a 2002 2900 SCR with twin v-6 and Bravo III's. Went out this past weekend in mild chop and at any speed above 30MPH the boat porpoises pretty bad. I had the OD's fully down and tried to correct with the trim tabs but it is a very uncomfortable ride. Seems like the boat is very light in the bow. Anyone have any thoughts or experience with this? My old 27 ft searay rode much better and that had a 100gl water tank under the forward V-Berth.

Anyone ever experience this and have any solutions?? :?: :?:

[seapuppy]

Hi Marty and welcome to the zoo....I have the 2700 scr and on similar water ..my porpoises too...but I put the trim tabs down a bit and bunp set the drive up a touch to get the boat trimmed out ..thats about it...try putting your trim tabs down..you may even need to have larger tabs put on....hope this helps and welcome to the zoo..

[martyc]

Thanks. I assume I have stock trim tabs but will check.

Ever try or consider adding ballast to the bow? Water or lead? I may attempt this but am looking for input from members who have the same issues.

Thanks :idea:

[seapuppy]

well..mine will porpoise for sure under the right conditions....but putting the trim tabs down will stop this...just need to bump them down a little at a time till it stops.....I haven't added ballast to my boat...remember that the more weight you add the more it's going to cost you in fuel.......
keep us informed...

[jimbenton]

Hi Marty, I have an 06 2900 and from what I have learned the 2900 will porpose a little more than some other boats. The Deep V on these boats are 21 degrees, a lot of boats this size are 18,19 degrees, so the bow doesnt sit up on the water the way lesser degreed boats do. Also the 2900 seems to be rear heavy as well when your running twin screws.

I used to raise my drive a little in my older 25 to get optimal planning, this doesnt seem to work with the 2900 unless the water is glass smooth.
When your running in chop make sure your drives are all the way down and start with zero tabs. Once up on plane tab up just a little on both sides until the boat stops most of the porposing. It will always do it a little in choppy water. Another way to further reduce the porposing is not to run directly into the waves , hit them on an angle, you'll be surprised at how much smoother the ride is. You dont want to add any extra weight to the bow but if you are carrying a cooler move it downstairs this wieght is already on the boat. filling up the water tank only half way helps as well.
Depending on the type of chop your in, you may want to back off the throttle a little, its better to go slower ,save gas, and enjoy the ride.

ps..
Dont forget to raise your tabs once you dock if you forget; getting back up on plane next time youre out will be more difficult with this boat. Ive found that getting on plane is easier if you dont dump both throttles all at once, instead roll on easily and get a little water moving under bow before youre at WOT ( wide open throttle ) kind of a slower dump...lol

Hope this helps

[JMHere]

Reading through all the article on here. Selling my 1996 2700 SCR and looking to to a 2000 or newer and am considering the dual 4.3l. So this is interesting to hear about the porposing. I havnt had any issues like that in my 27 with single 7.4l bIII. I do however keep a nearly 100lb spare battery under the forward berth though.

[pascavone]

As for the revised question, 2- 4.3 or 1- 7.4, i've talk to both owner and then performance is similar, just a bit more maneuverable with two props for docking...

They did not make a 4.3 V-6 fuel injected until 2004 or so, so i when with the 7.4 MPI, with 1/2 the maintenances of two engines...

to the old 2007 post below:

since you just got the boat, my guess is your tabs are not working correctly, stuck, or hanging off the boat.

Not uncommon to have a failed hinge after 10 years, I replaced both my tabs with new, and new cylinders.

There no way for a boat surveyor to tell if they are extending evenly and correctly.

I would go for a swim at the dock, and let someone run the switch (with the engine off), and use your hand to see if the tabs are running out correctly.

[shrew]

mmm another zombie!!!

Porpoising is not a product of the size of the boat, the size of the engine, or whether it is an outboard or an IO. I occurs much, much less frequently on inboards. It is by and large a result of either too much drive trim out, or not enough trim tab down (or a combination). It's actually more common in smaller boats without trim tabs. Most commonly it is because the drive it trimmed too far out. This causes it to try to keep raising the bow. However it will only go so high, then gravity brings it back down again. It "Yo-YO's" like this or 'popoises' as it's commonly called.

Use more trim tabs, or tap the drive in a bit. That should reduce this problem.