Porpoise ! Agian!

[FoMoCo]

OK I am still scratin my head! My 1977 18ft Kachina was Workin perfect until I went to Camp Far west to do a full pass, like more than an 1/8 mile spurt. With the short pass with about 1inch of chop it would do 76 MPH! But I wanted to see if I got any lift when I legged it out. It would go along just fine like with the normal short runs , but after like 1/8 mlie it wld start to porpoise again!! I tried it several times to make sure it wasn't just the water. It wld do it sooner on flat water! What gives? the pumps at the stock angle, with a Ride plate set at 0 degrees, and a 1/2 inch back Cut MPD shoe. The grate is also and MPD open center loader grate! What can be sucking the boat back down? I am thinkin that a Droop and a Diverter would make it worse? Help, I don't know where to go from here!! Is the boat posessed??!!

[RR1/ 001]

Put some "down" in your ride plate, it will take the porpoise out! Start at 1 degrees and go from there.

[HBjet]

I would bring that ride plate up a few degrees to start with. Try it at 3, and then go from there. Also, a diverter will help you out for sure, that is there main purpose. You don't need a droop to install one. I run my plate at 6 degrees, and I use my diverter to trim.
HBjet
[This message has been edited by HBjet (edited April 23, 2002).]

[Licketty Split]

Check the hull for any hook, I hate to sugest that ;(

[FoMoCo]

I messed with the ride plate and got it to quit Bouncing when I was using an ANgle iron type intake grate, the boat was only pushin like 74 mph. But When I put the mpd open center loader grate the boat responded with massive amounts of mid range and 76 mph on top end! I recently got done with this 3 year project which involved having her upside down , and showed no sign of a hook,( I used a flat obect about 4.5ft long) There was no hook at least the back 4.5 ft didn't have one! I have seen other hulls run with out rideplate or shoe, but with a droop and diverter pointed all the way up run at full throttle and not porpoise! Am I missing something in my combo? I know its pushin 500 HP, I an runnin 5400 rpms with a B+ imeller, and a little 429 BBF

[DickDanger]

I'm thinkin' that the Ford is the problem. Here's what to do: make a trip to Niagara Falls, take the 429, and launch it from the top. Should smooth the porpoise right out.
Hahahaha...only kidding you. Take care. -DD out

[Blue Panther]

I have a 17' - 81 Haskell and did not really porpoise a lot only when there was more than 6" of chop, but I am only pushing 60. I got a new 350 chevy engine and decided to rebuilt my jet and add a place diverter get reverse and better ride thru chop. I now push about the same 65mph and I can tell you the place diverter is a well worth money!! I handles so much better I can turn in a idle without moving from a my orgin. Also in chop I have total control of how much water to force my nose down. Do you really think ride plates are that are about 6-8 inches are going to add enough length to your boat to stop the force of your HP coming out of the jet?? This is what I was asked! My answer was people buy it, it must do something. Well on smaller boat, it might so something but mostly I sore thumb! Use you Hp to help push to boat forward and keep the nose down at the same time. I spend $1500 for my rebuilt with the place diverter added to it.....The best money I have thrown into my "whole in the water," well it is not really anymore!!!!

[Hollis]

Especially if you can use the "Trim-A-Just" electric trim control. However it may be just for the 12JF pumps.

[Old Guy]

FMC if your ride plate is not stiff enough, it will bend and create a hook big enough to cause porpoise. Does your ride plate have turned up edges or stiffeners?
old

[SOUTHWIND377]

Go with the diverter and it should fix your problems, if you go up with the rideplate the boat will porpoise more unless your are in the throttle, by using a diverter it will allow you to run 3-4 degrees up on the rideplate and get the lift for top end runs but when crusing you can go back down with the nozzle and get away from the porpoiseing. Thats just my 2 cents.

[FoMoCo]

Are you saying my boat would be faster, with more up angle on the ride-plate and then I put more down thrust force with the Diverter? I know from testing that it will porpoise sooner with ride plate up!

[HBjet]

I have my 19' boat setup with 6 degrees up on the ride plate, and I use the diverter to eliminate propoise. When I'm at WOT, the boat tracks nicely. When I cruise, I angle the diverter down and everything is smooth. IF you adjust your ride plate down, at WOT your boat won't get the lift it should and you will loose top end mph. That's why I suggested raising it, and then use the diverter for trimming.
Here is a photo of my boat at WOT, with my ride plate 6 deg. up, and my diverter 2 notches from all the way up.
http://home.socal.rr.com/boatbutts/Going.jpg
HBjet

[FoMoCo]

How fast, and how much horsepower are you runnin in that thing? Just curious for comparison???

[HBjet]

The only time it was radared, it was 71 and that was after a 1.5 stage blue print. The motor in that photo is basically stock 454 .30 over with a tunnel ram, and dual holley 450's. The motor makes 450HP I'm guessing. This year I hope to get a GPS and see some real numbers, who knows, it could be slower.
HBjet
[This message has been edited by HBjet (edited April 24, 2002).]

[SOUTHWIND377]

Just to give ya a little idea of ride plate adjustment mine was 1 degree down from shoe I raised it to be 4 degrees up from shoe. I was running 82mph 1 degree down, breaking water way in front of the motor. I moved it up and gained 5-6mph at WOT and was breaking water right at the rear of the motor. I don't have a place diverter I do all nozzle adjustments with wedges. The boat will porpoise bad unless you give it the throttle. So in your case being a lake boat you will most definetly want to invest in a diverter so you can go up on the rideplate and still be able to cruise around by adjusting the diverter. Just my 2 cents again. Later

[FoMoCo]

Strange, I hope mine will respond that well! OK Now I think I am confused. My boat starts to porpoise at the top end as it sits now! when the plate was up it wld just do it sooner. Is thisjust like your boats? Hey SOUTHWIND377 what angle is your nozzle at? Is your boat a V-bottom or a tunnel southwind? Sorry for all the Questions but this is worring me because I just spent 3 years on this project, I dont want to think the hull is no good! thanx!!!