tri-hull bounce

[V153]

Re: tri-hull bounce

I'd raise the motor 2 holes. (One hole = 3/4")

 

[smokeonthewater]

Re: tri-hull bounce

well this is rare but I'm gonna disagree (for now) with EVERYONE..... looking at the last pic the angle looks fine to me... the motor is maybe a bit on the low side but shouldn't be enough to cause a problem other than the loss of a SMALL bit of top speed and while smart tabs might be nice to have you shouldn't NEED them just to control the boat and get on plane.

Lets explore other things for a bit.... sight down the keel and use a straightedge and look to see if you can find any sign that the hull is misshaped... also step on the lower unit of the motor and jump on it.... look to see if the transom flexes AT ALL... I hope that I'm wrong here but let's cover the bases.

 

[paul33]

Re: tri-hull bounce

Hey Kevin

i went back to my boat and stood on lower unit of motor with my 230lbs and jumped up and down and there was no deflection in the transom, the boat just bounced the trailer up and down. also sighted down the keel and it looks sound.

i guess i will raise the motor and try her in the spring when the lake softens

Thks Paul

 

[smokeonthewater]

Re: tri-hull bounce

Ok that's GOOD

is there any chance that you were trying to plane it with the engine trimmed up? Just to be certain you DO understand that it should be all the way down like in your pics and that you don't start trimming up until it is up on plane.... Also that going to far will cause it to porpoise IE "bounce".... I'm not trying to say that you did anything wrong, just looking for any possible cause for your issue.

If you had your hand on top of the prop and you moved it up you would hit the anti ventilation plate ... that surface is what folks are telling you should be even with the keep or slightly above.... I still doubt that (as close as yours appears to be) that alone would cause this issue.

 

[Part-time]

Re: tri-hull bounce

The motor looks a little low on the transom... nothing that should cause purpoising. If anything it would just hurt top speed, wich you're not even getting at.
Loose the hydrofoils, they are for overweight/underpowered pigs to get up on plane. They should be out of the water once planed out.
When it starts purpoising, does the rpm stay the same or does the motor rev up and down with the bouncing.
If it does it may be the wrong prop and it cavitates way to easy or it could be a prop that spins on the hub when too much load is applied.

 

[paul33]

Re: tri-hull bounce

Well i do start out with motor all the way down and bow is way up(would that be the hydrofoils?). i believe its was porpoising with motor trimmed down. i did put a new prop on it cuz on one of my trips i lost the original prop. i know sell it and cut my losses. lol. i will try raising it a bit and see how that goes. its great boat for pulling tubes i wore my 18 yr old nephew out in 10 minutes.


I appreciate all your guys help.


thks Paul

 

[southkogs]

Re: tri-hull bounce

i know sell it and cut my losses. lol.

You're no where near that yet. Those hulls are fun to play with - I had a 15' for years and loved it. I'm now on a 17' with an I/O. Worse you're gonna' have to do is keep yours throttled back.

 

[paul33]

Re: tri-hull bounce

ya i got it late last year so didnt get out much so i cant wait for the spring. i have to locate a pylon for it, it has the cleat on the floor and the pins on the top of sides towards the back,so one of the owners mustve had a pylon but it didnt make it to me.


thks again everyone, you guys are great and have given me a start on my boating education.

Paul

 

[smokeonthewater]

Re: tri-hull bounce

the bow will always go up until you get on plane and if you aren't ABSOLUTELY CERTAIN that it was porpoising while trimmed down then you might not even HAVE a problem..... the fin(s) would have potentially made the trim adjustment VERY touchy and added to your frustration.... If you haven't run it since removing them then give it a try before raising the motor higher on the transom..... only change one thing at a time, that way you will know which change gave which result
this is a bit of an extreme example but it gives you an idea of what normal looks like....
http://www.youtube.com/watch?v=TCibnLzWU74&feature=endscreen

Also if you are trying to speed up gradually accelerate you will likely have issues..... smoothly apply throttle (lots of it) until the boat planes and then back off to achieve your desired cruising speed while keeping at least enough to keep the boat on plane

 

[chriscraft254]

Re: tri-hull bounce

I will say it again, Nauticus Smart Tabs.

 

[southkogs]

Re: tri-hull bounce

I will say it again, Nauticus Smart Tabs.

LOL - go look at the boat in Chris' link. He'll have you put the smart tabs on first ... then the light show gets installed ... heated cup holders ... etc, etc ... BOAT BLING!!

He's serious about the tabs ... I'm just playin' 'bout the rest.

 

[paul33]

Re: tri-hull bounce

Ok so I'm guessing Smart tabs might help? I am thinking about a stereo install but may pass on the heated cup holders lol

Thks Guys

 

[oops!]

Re: tri-hull bounce

smart tabs will help any boat.....as the are a extra control surface, much like a trim adjustment on an airplane.

i mentioned them in my very first post.

but i really think we should find the problem with your rig.....this is not normal.

first thing ...i would adjust the angle of attack on your motor.....try setting up the angle in the last hole. and see if it stops the bounce.

 

[smokeonthewater]

Re: tri-hull bounce

Yep, I agree on the tabs too but as I said above, we need to fix your issue first and then add them

 

[cyclops2]

Re: tri-hull bounce

Hi guys.

I enlarged his last picture #3 to 200%. I think he has the depth finder black plastic pinger too close to the feed water to the prop. It could be causing the Porposing by breaking up the water flow too close to the prop. No real need to put a pinger within 16" of a prop.

Rich

 

[paul33]

Re: tri-hull bounce

Ok my first boat and I went by instructions and ya I put the depth pinger there, could that really be my issue? That would be to easy.

 

[smokeonthewater]

Re: tri-hull bounce

transducer....... I doubt it but easy to test

 

[cyclops2]

Re: tri-hull bounce

Do not feel bad Paul.

I did the same thing on the 16' Aluminum Lowe 15" short shaft boat with a 9.9 hp engine. NO PROBLEMS.

Put the the 35 hp motor on centerline & the 9.9 hp as a side mounted troller / kicker. Every time I approached getting on plane the 35 hp would surge / slip/ cavitate. Finally my 2 stroke mechanic took a look at the Pinger/ transducer. Said just undo enough pinger & cable to lay it safely in the boat..............Bingo ! Boat was scary fast.
I could feel the rumbling growling surging of the prop as it would grab & slip back & forth. If I slammed the throttle to WOT, the ride was almost sitting still in froth. DO NOT go to WOT as I did. Could have blown up the 35 hp easily. I got lucky.

Rich

 

[Philster]

Re: tri-hull bounce

Paul...

1) I've seen you say that you get on plane with the motor trimmed all the way down/in, which is correct, but then you indicate that it porpoises with the motor trimmed down/in. I am assuming you trimmed out and it porpoised that way, too? Why I ask: Sometimes a boat will porpoise if trimmed down/in when running fast, because you are just slamming the bow onto the water, it bounces off, and then the cycle repeats. If this is not the case, move to 2.

2). My hunch: The motor height is going to have to be slightly different on that hull configuration. In my opinion, this is the most likely issue. That hull might require a slightly different than standard rule-of-thumb mounting height. Others have opined that it might be close to what would be considered 'normal', but my honest opinion is that your motors final height should be different than rule-of-thumb, because of the shape of the hull. It's not a true stepped hull; we know that. However, I do believe it requires the motor height to be mounted higher or lower than what is traditionally considered 'normal'. Boats with different types of water action off the back, due to the somewhat unique hull designs, often require some stray from a standard mounting height.

 

[cyclops2]

Re: tri-hull bounce

Paul

The most obvious Question ?

Did the boat do this jumping up & down before you put the a transducer on the boat ? Did it do this when you test rode the boat ?

Old brain is getting realy slow.

Rich