How do I stop the PORPOISE? [Archive]

WriedtStuff

06-17-2007, 02:03 PM

That constant bouncing is driving me nuts. I can drive thru it...but then I really only have 2 speeds. Slow and trimmed almost all the way down...and wide open and trimed way up.
The prop I have is a 22 pitch stainless thru hub dog ear. I don't really know what brand. There are no markings on it.
The boat is a Stratos 18' Tunnel Vee, with a 175 Mariner.
Is there a jack plate adjustment that will stop the mid speed propoise? What other adjustments can I do to calm down the porpoise?
Suggestions?

3:30dirty

06-17-2007, 07:12 PM

Never dealt with that problem on a boat of that length, but sounds like maybe your motor is too high....may help to play with the motor height. Might try screaminfly.com for more outboard help!

Beer-30

06-17-2007, 07:34 PM

If it's anything like an outdrive, leave it down to start. Trim up until it porpoises, then trim down until it stops. Porpoise at speed is a function of being "over-trimmed".

Tom Brown

06-17-2007, 08:51 PM

You could easily have too much prop there. What is your WOT RPM?

WriedtStuff

06-18-2007, 04:38 AM

Over 5k rpms.

Paul128a

06-18-2007, 06:27 AM

I used to have the same problem on my 21 foot v-bottom sterndrive. I bounced around a lot at mid-throttle. I tried to move weight around, but the best solution were Bennett Trim Tabs.
By the way, there are thousands of those minitrucks running around here in the Philippines, converted to LHD. I even made a jetboat using a supercharged F5A engine. :)

Tom Brown

06-18-2007, 12:28 PM

Over 5k rpms.
You might want to try a smaller prop, perhaps 19p, or so. You should prop so you get around 6K WOT.
My boat does the same thing with three people in it but doesn't do it when it's just me or me and someone light. The prop is trying to lift the bow but if the boat is too heavy, the prop won't be able to hold it up there. The solution is to send more water past the prop (lower pitch) or run a prop with less bow lift.
I'm jacked well above the pad with my prop shaft (about 1.75") and I could trim up so I can't see over the bow, if I wanted.

Forkin' Crazy

06-18-2007, 07:35 PM

On a tunnel I would guess it is a balance issue. How much set back do you have?
I had a tunnel that the bow was so light you could pick the boat way up in the air by the sponson. But I sat way up in the front... I would porpous like normal tunnels do. I would fly the bow really high (must be careful of head winds) and it would slow to a slow lope.

Paul128a

06-18-2007, 07:41 PM

Oh yes, I also changed to a straight back prop (cleaver) as the round ears tend to lift the front end high.

WriedtStuff

06-19-2007, 05:28 PM

You know what's funny? I have posted this same question on 2 other boards, and I can't believe how many different answers I have gotten. From boat is too heavy to add weight to the front. Prop is too small and need a bigger prop. Jack up, Jack down.:confused: :confused:
I guess it is just going to be trial and error.
I measured my setup and I was 2.75" lower than the pad with the center line of the lower unit...so I raised it 1". I figure this change will be fine since I have almost 20" between the pad trailing edge and the lower unit leading edge...because the boat has a built in setback on the transom and I am running a 6" jack plate.
I guess the biggest thing I need to know is a base line to start with. like what is the OEM recommendations for the prop size...where can I get this type information?

Ike

06-19-2007, 05:59 PM

Well you now know that porpoising is not caused by just one thing. It can be a combo of things. They first should be making sure the hull is blueprint flat in the planing area. Any convex or concave can cause porpoising. You should be able to lay a stright edge on the hull (foreward and aft) and it should be dead straight.
Check your weight distribution, check your set back, check the height of the motor on the transom. Do you have a jack plate? Can you raise and lower the engine? A study done by Mercury (I think it was mercury, sorry if I got it wrong) showed that a lot of porpoising is due to slack in the steering system. There should be no slack at all. I honestly don't think it is your prop, but it could be. If all else fails try that.
Back to weight distribution. Where is your fuel tank? If it is low in the boat, amidships or near the stern it's probably ok, but if you have a bow tank it might not be. As you use gas the tank weighs less and changes your center of gravity which changes the center of force on the hull when at speed.
ANyway. keep trying untill you hit it.
Oh yeah I forgot trim. Trim can have a serious effect on porpoising. Try various trim angles.

Tom Brown

06-19-2007, 06:45 PM

... Prop is too small and need a bigger prop. Jack up, Jack down.:confused: :confused:
I guess it is just going to be trial and error.
Be careful with a bigger prop. If you're close to 5000 RPM now, going larger is going to lug your engine even more and 2 strokes tend to consume pistons when they lug too much.

Forkin' Crazy

06-19-2007, 07:18 PM

What Ike said about the bottom being straight is right on. A hook can cause a porpoise.
Loose steering will cause a chine walk, not a porpoise.
Lets see some pics of the boat. Is it a mod VP? Does it have real tunnels and sponsons? What year is it and the motor? The more information you give, the better the advice. I am no set up guru, but I have set all my boats up, granted it took a several tests to get it right.

Forkin' Crazy

06-19-2007, 07:19 PM

Oh yea, do you really drive one of those red tractors? If so, I know the problem. You have a SCREW loose between the steering wheel and the seat!!!:jawdrop:
:) :D :D ;)

WriedtStuff

06-20-2007, 05:21 AM

Ike,
My setup is described in the post above yours. Both my gas tank and battery are in the back as they were install by the manufacturer. I do have a jack plate as mentioned in an earlier post. I have also moved the engine up...1" but have not tested that yet.
I have dual cable steering and it is as tight as a drum....I agree with FC, as I don't think loose steering would have anything to do with Porpoise...chine walking maybe.
It is a Stratos Tunnel VEE......I am not sure was a Mod VP looks like, but my boat rides on 3 points....a center pad like a standard V-hull and 2 sponsons like a tunnell hull. I will try and get some pictures to better describe.
Hey Crazy.....What's wrong with my tractor? Do you even know what kind of tractor that is and how much it cost? I have 5 of them. But I don't drive them.

Forkin' Crazy

06-20-2007, 07:00 AM

Put a long straight edge on the running surfaces and check to see if they are straight.
Yea, it is a RED tractor--- IHCase, Case NH, or what every they call themselves now. And I guess that depends on how many hrs and what size. I never buy them new.... just try to buy a low hours and good shape. I am looking at getting a 8410 maybe this fall or maybe a Challenger. So yes, I know how much they cost! ;)
BTW I do drive mine, and green is the shizzznit! :cool:

WriedtStuff

06-20-2007, 05:14 PM

Forkin' Crazy

06-21-2007, 08:19 AM

MASSEY FERGUSON!!!!:D
AKA MF. And we all know what that stands for !!!! ;)

bbc540

06-21-2007, 01:47 PM

If you have a water preasure gauge keep an eye on it as you raise the motor if not I suggest you get one and raise the motor 1/2" at a time until you see the water preasure fall off slightly then lower it 1"
different props react differently try some of your buddys maybe a 24 I personnaly like a chopper but thats me then there is cup rake diameter so much but I think your problem is the prop but again thats my opinion.

WriedtStuff

06-27-2007, 08:05 PM

I talked with a perfomance propellor shop and they suggested I try a 23 pitch 4 blade prop and raise the jack plate some more....do you guys think this will help?

stoker22405

07-02-2007, 01:15 PM

Buy a new boat

Tom Brown

07-02-2007, 01:35 PM

... they suggested I try a 23 pitch 4 blade prop and raise the jack plate some more....do you guys think this will help?
I'd jack it before you try a new prop. I suspect jacking will help a lot more than the prop.

Forkin' Crazy

07-02-2007, 01:39 PM

I'd jack it before you try a new prop. I suspect jacking will help a lot more than the prop.
I'll agree with that, but what kind of prop is on it? Got a digital camera? Boat pics may help also.
Usually 4 blade is a smaller diameter, so that may help in reducing bow lift, depending on how much cup and rake it has.

WriedtStuff

07-03-2007, 10:35 AM

I am not sure the make on the prop. It is a 21 pitch..is all I know.
I just bought a Laser II 22 pitch off ebay, and was going to try it...but outside diameter of the hub is about 1/4" smaller than the 21 pitch prop...so when I mount the Laser, it has a gap all the way around between the prop and the housing of the lower unit....is this prop going to work? I have run "over the hub" props before, but this is "thru the hub" prop with gaps that will allow the exhaust to go over the hub also. And it is already a vented prop.
I will try to get some pics tonight.
Also, how do I tell if I need a new thrust washer? When it is totally gone?

WriedtStuff

07-03-2007, 03:26 PM

Old Prop
http://i133.photobucket.com/albums/q44/maxum25/DSCN0271.jpg
New Prop
http://i133.photobucket.com/albums/q44/maxum25/DSCN0270.jpg
See the gap around the prop.
Now here is my current setup.
http://i133.photobucket.com/albums/q44/maxum25/DSCN0276.jpg
http://i133.photobucket.com/albums/q44/maxum25/DSCN0277.jpg
http://i133.photobucket.com/albums/q44/maxum25/DSCN0275.jpg
http://i133.photobucket.com/albums/q44/maxum25/DSCN0279.jpg

Forkin' Crazy

07-04-2007, 11:27 PM

The smaller barrel of the hub will allow exhaust to ventilate the blades, causing it to rev up when coming on top. This is good if you need it, i.e. like when using a larger pitch too keep it from lugging out of the hole.
Looks like a ModVP hull. Did you ever put a straight edge on the center pod or sponsons to see if it has hook in it?
Nice boat, BTW. :cool:

Forkin' Crazy

07-05-2007, 07:28 AM

However, for top end performance you will loose some mph. as the smaller hub creates more slip.
....um.... That is not true. It is a lot more complicated than that.
BTW Thrust washers will last a long time. The only time I have had to replace one was when I spun a hub and it damaged the washer.

Forkin' Crazy

07-05-2007, 10:14 AM

At speed the exhaust doesn't "climb" up the blades. Take an over the hub prop for example, all the exhaust flows on the outside of the hub.

WriedtStuff

07-05-2007, 11:59 AM

I should have turned the prop so you could see it is a Laser II. It already has vents in it...I'm just curious if the vents and the smaller hub will be too much slip. Guess I will just have to try it and see.
Oh. my engine has has the exhaust ported just above the cavitation plate. I have to assume some previsous owner did this. There are 5 3/4 diameter holes drilled in the mid section just above the plate...so the exhaust blows straight down onto the plate. You can see the dark sooty spots in my pics above.

Forkin' Crazy

07-07-2007, 12:49 PM

If he drilled the exhaust, you shouldn't have much problem coming out of the hole.

kylesbds

07-07-2007, 07:02 PM

boats&bars

07-07-2007, 11:55 PM

I have a 14/12 x 17 stainless brand new been on the boat once
btw you are way overpropped by atleast 4 pitches let me know $ 200 obo

Forkin' Crazy

07-08-2007, 09:24 AM

I have a 14/12 x 17 stainless brand new been on the boat once
btw you are way overpropped by atleast 4 pitches let me know $ 200 obo
It is not new if it has been on the boat. :idea:
"Way over propped".... LOL! You're pretty good at determining that. Maybe you have an answer to his porpoising problem? :idea:
SPAM! :crossx:

Forkin' Crazy

07-08-2007, 09:25 AM

WS, send me a PM.

boats&bars

07-08-2007, 08:13 PM

It is not new if it has been on the boat. :idea:
"Way over propped".... LOL! You're pretty good at determining that. Maybe you have an answer to his porpoising problem? :idea:
SPAM! :crossx:
I had the same stratos fish & ski with a high 5 that had the same problem
changed props and it went away......... just trying to help:jawdrop:

WriedtStuff

07-09-2007, 03:57 AM

There is no way I am over propped....I am turning 6000 rpms with a 21....if I went to a 17 it will way over speed the engine.

WriedtStuff

07-09-2007, 04:03 AM

WS, send me a PM.
For some reason I cannot send PMs. Send me one...or email me from my profile/signature address.

Forkin' Crazy

07-09-2007, 07:25 AM

Can't do either. Me thinks you need to go to UserCP and change some options. ;)

Forkin' Crazy

07-09-2007, 07:25 AM

I had the same stratos fish & ski with a high 5 that had the same problem
changed props and it went away......... just trying to help:jawdrop:
;)
:D

WriedtStuff

07-09-2007, 12:55 PM

Can't do either. Me thinks you need to go to UserCP and change some options. ;)
There is no option for PM in user CP...email to
maxum25@gmail.com
Thanks

Forkin' Crazy

07-26-2007, 09:42 PM

I sent you an email at least a week ago???:eek:
:confused:

sorry dog

07-29-2007, 11:59 AM

You'll know the first time you try to plane if that prop will work or not. My guess is you'll peg the tach for the first 30 feet and then the prop will get enough bite and be fine after...but if the boat is too heavy then it may not get enough bite to catch.
An easy way to experiment with weight is to go buy 100# sand an try that.
I've run a couple of Laser 2's and thought that they were good all round props.

73kona455

07-29-2007, 09:53 PM

The Lazer 22 pitch that you bought I think is the wrong prop for your lower unit. Mercury and Mariner had a 4 3/4 gearcase and a 4 1/4 gearcase. I know this cause I have a Mariner 150 that has the 4 1/4 gearcase and a Mercury 200 that has a 4 3/4 gearcase. It just depends what size it is. The props are interchangeable but they both have their intended uses. When your prop is off measure the diameter of the gearcase I bet it is 4 3/4 and the prop you bought is 4 1/4. It will work but you won't have the best results.
i have run a small barrel prop on a large diameter gearcase for years without any problems or performance loss...with his exhaust relieved above the water the exhaust coming out the hub is greatly reduced...now think about the amount of water flowing over the gearcase....do u think this small amount of exhaust exiting around the prop is really gonna cause a problem?..the water flow will be alot greater than the exhaust flow.........:eek: :rolleyes:

73kona455

07-29-2007, 09:56 PM

i think i would start by lowering the motor on the jack plate.. and start moving it up a little at a time till you find the sweet spot where it will carry the bow with no porpoise....take it to the lake and play with it till it works right

WriedtStuff

07-31-2007, 08:24 AM

Did some testing.
PowerTech TRO4 23P. - 5500 Rpms WOT 55.9 MPH.
Laser II Small hub 22p - 6000 RPMs WOT 55.0 MPH
Unknown Brand 21p 3 blade large hub - 6000 RPMs WOT 58.7 Mph.
None of these props made an difference in the mid range porpoise. Well let me say that the 22p Laser seemed to have a little less bounce, but did not stop it.
So what should I have learned from this experiment?