Need ideas to stop porpoising?

gss036 · #1 07-20-2008, 07:53 PM

Got the new Honda 225 installed and have 10 hours on it on my 1989 Seacraft 23WA. When there is a little roll on the water the boat tends to want to porpoise. I had moved 20 # lead up front in the anchor hole in the bow, after yesterday still doing the same, added another 40# lead. May get out again Tue or Wed. The 225 has awsome power, but you do know you have the extra 220+# on the back compared to the 200 hp Merc. I have about 6 hours on the current fuel, so will fill it up again when I go out to get an idea of fuel burn for the 6 hours running. I am running a 15 hp Honda off the main tank, but that thing does not use a lot of gas just trolling.
I am not getting any water through the scuppers, sure need to watch the big wakes from the stern, if you can't get turned in time. I do get a little water into the engine well with the wakes, but they drain right out. I had to pull the hatch and reseal it good as the engine installer had to replace the old one because of the orginal engine bolts and did a lousy job sealing it.

JohnB · #2 07-20-2008, 08:00 PM

Is the motor trimmed all the way down, and is it mounted at the right height? Too low will cause some strange things. If you mounted it at the same height/hole as the 200, you have a couple of hundred extra pounds on the back now.

Trim tabs? do you have them?

Move the batteries forward?

If all else fails, bracket?

You might want to check the transom for wetness, if it's soaked, it will add a bunch of weight back there too.

gss036 · #3 07-20-2008, 09:27 PM

Yes, I have trim tabs, but hate to use them as the do slow you down 2-3 mph. The transon is bone dry as the boat is stored inside anytime it is not in use. I hope the xtra weight in the bow will help and I will just have to learn the new handling characteristics and make adjustments.
The engine is mounted in the same holes and height as the old one, position looks good. It does put out quite a boil when slowly accelerating. 14.25 X 17 SS prop gives me around 30mph @4000rpm.

Bigshrimpin · #4 07-20-2008, 11:48 PM

doel fins or permatrim. Try removing the 15hp just as an experiment (that's another 120 pounds). If you're not getting enough negative trim . . . then you can always install wedges.

How's the speed compared to the old 2.4L 200hp merc?

FELLOW-SHIP · #5 07-25-2008, 12:30 PM

Quote:

I have trim tabs, but hate to use them as the do slow you down 2-3 mph.

Hi Gary;

Been reading all the good info which is all very valid but you are avoiding using the TABS which is the answer to your problem. All boats designed and made from the factory are tested with light loads and no extra weight. As time goes on we add and change all kind of things. Shift weight and adding stuff like kickers and 220 Lbs. for today’s newest 4 stroke motors, large live wells and what ever else we think is cool. Gary you need to look at Tabs like pilots look at flaps on a plane you just need to use them to control your boat the way you want it to run.

Fellow-Ship

Just for the Grins

Captainkass · #6 07-25-2008, 11:05 PM

Hey G, do you have a long shaft on your new motor if so this can cause some porpoising if its not the right height in relation to your transom....

gss036 · #7 07-27-2008, 03:59 PM

I was out again yesterday and it was a fairly calm day, had two of my late-teen grandsons w/me and I had moved a total of 60#'s of lead to the front of the boat. To my surprise, the porposing has just about (90+%) gone away. The first few trip we had a lot of chop and rolling water and that may have had more to do with it than anything. I did lower the trim tabs slightly, don't know if the were even or not had not set them prior to going out. As soon as things calm down around here and I have time I will dig more until the problem is solved.
I know I had a friend who had a Wellcraft w/225 Suzuki on a bracket and he had really had a lot of porposing on his boat. He has since sold it so I doubt if he ever solved the problem there.

McGillicuddy · #8 07-21-2008, 03:36 AM

All of these responses here are valid but unfortunately none of the offered solutions will cure every porpoising problem. And yet every one of them will resolve many such problems. Changes along with your observation will help. You mentioned your 225 is 220lbs more than previous motor - that is significant. Did you have a fin on the old motor? I could definitely see a benefit to such in the windy chop of the Sound. Consider four holes in your new motor. A hydrofoil like a Doel-fin or Stingray or SE Sport 300 will help you plane faster with out drag, but at 30 mph trim tabs will not be the efficiency burden you might think and when properly trimmed they will help dramatically in a heavier 23' that maybe overweighted astern.

Weight definitely needs to be re-distributed. Remove the kicker as Bigshrimpin suggested - that is far more significant than adding 60lbs of lead in the bow - and remember the kicker sits back a foot behind the transom. Remember the teeter-totter back in school -- slide farther out from pivot point and you could outweigh the bigger guy, granted not a problem now, Big Fella

. Besides who needs a kicker with that gas-sippin Honda. Is your idle too fast for Salmon?
If you use a bait tank try running with different amounts of water in it, 30gal is about 240lbs, might need to move it fore or aft.

I've never seen a 23WA but it does sound like the rear end needs to get out of the water a bit. Maybe a stern-lifting prop is helpful. If you are avoiding the trim tabs only for efficiency loss, experiment with them a bit. First make sure they are not set all the way up, if so, I'd wager that's half of the problem. Take a straight edge and set them parallel,or inline with the hull. At the very least it will make the boat believe it's a foot longer. Boat racers in Miami used this trick in the old days. Just an extra foot of stainless plate flush with the hull...It ain't rocket science - just hydrodynamics...whatever...

If you had bad seal on the mounting bolts (assuming they went through the transom) You might get a moisture meter on the transom. Salt water attracts moisture and I know its wet up there most of the year so even though you store in shelter, if it gets wet it stays wet awhile... Sorry to ramble. Good Luck

1bayouboy · #9 07-21-2008, 08:48 AM

If you're going to try a stern lifting prop I'd recommend a Rev 4.

JohnB · #10 07-21-2008, 11:19 AM

A lot of good ideas here, IMHO, it's a balance issue. I haven't heard of anyone having this type of problem with a WA/Cuddy, usually just the CC's. I would try removing the kicker, and see if it get's better, if it does, than it's a balance problem. I don't remember where the gas tank is mounted in a WA, but if it's mounted too far back, and is full, that is something you might want to look at. I know when my in-transom livewell is full, 44 gals, it really screws up the balance. These boats were designed very well, and IMHO, anything past 450 pounds of motor on the back really gets them out of balance.