Please help with Tahoe porpoising

[Jshadwick]

My brother has just bought a 2001 tahoe with a 4.3 i/o. We have always had fishing boats so the inboard outboard is new to us. The problem he is having is the boat will porpose like crazy, and we start off with it trimmed all the way down. I dont mean it bounces up and down alittle, it feels like it is jumping out of the water. I am thinking it is the prop. It has a huge SS prop that reads 10319 m1419. The guy he bought it from said he hit a rock with the old prop and hasnt ran it with the new prop. Once we get over 40 mph it rides smooth and it tops out right over 60, according to the spedo in the boat. So, any help with this problem would be great. He hopes that he doesnt need trim tabs. Thanks, Jeremy

 

[ezmobee]

Re: Please help with Tahoe porpoising

What happens if you move some weights forward? If its a bowrider, does it go better if there are some passengers up there?

 

[DuckHunterJon]

Re: Please help with Tahoe porpoising

Lot's of things it can be. As Ezmobee said, start with ballast. Have a couple people sit up front and CAREFULLY try it out. If that doesn't work, try different trim settings on the motor. Does it have a hydrofoil fin on it? If so, remove it and try it.

Next might be trying smart tabs. They cure alot of problems. Another thing to look at would be the condition and shape of the hull. If it has a hook in it, none of the above will solve the issue. If you aren't familiar what to look at, take it somewhere that can.

As for the prop, I can't help you there - but it seems unlikely to me that the prop would cause it. Let us know what RPM's you're running at that top speed to get an idea if you are propped correctly.

 

[Susquehanna Squid]

Re: Please help with Tahoe porpoising

Is it porpoising or chine walking?

 

[Jshadwick]

Re: Please help with Tahoe porpoising

I guess you would call it porpoising. It feels like we riding a bull. I have never seen anything like it. I inspected the floor and couldnt find anywater damage. I think we will try the smart tabs and go from there. Thanks for the responces

 

[Maclin]

Re: Please help with Tahoe porpoising

Chinewalking is the stern of the boat literally jumping from one chine (edge of stern) to the other. If it does that very many times when you are hitting 60 you will be lucky not to be in the boating headlines the next day!

Along those same lines, are you sure the drive actually trims all the way down, do you use the tilt switch to get it all the way down to start? Then use the trim to trim up as you accelerate? When do you start trimming up? And how do you hit 60 if it is porpoising that bad at 40, I mean, WHAT makes you want to go faster

To troubleshoot further it may make sense to get a "stock" prop and see how it performs with OEM specs. Also, keep in mind (if I read your post right) the previous owner had not driven the boat since the prop hit. There could be more wrong with it than just what appeared to be a dinged up prop.

Good luck to your brother, here's hoping all of this is not the reason the previous owner sold the boat

 

[Jshadwick]

Re: Please help with Tahoe porpoising

I know that it sounds dumb to keep going with it riding so bad, but if he gives it full throttle it gets above 40 pretty quick and then it stops jumping. He bought this boat to ski and tube. If he backs down to about 25 mph or so, it rides smooth for about 5-10 seconds, then it starts jumping again. He found a local marina that will trade him a prop for his SS prop. So, he is trying it out today with a new prop, and they will keep letting him use different props until he finds one that he likes.

 

[Texasmark]

Re: Please help with Tahoe porpoising

Speed and trim position are correlated. Jshadwick just acknowledged that in the above post. For a given set of conditions and trim position, there is a minimum speed that you can obtain and have a stable ride. Above that, the ride is silky smooth in silky smooth water, obviously the rougher the water the trickier it is.

Below that minimum speed, the slower you go, the worse it (the porposing....bow bouncing up and down) gets. When it gets worse, either trim in (tuck the lower unit in towards the transom) or move some load forward. Not rocket science. Yes props certainly affect it, but the basic element is trim position vs speed.

HTH

Mark

 

[Jshadwick]

Re: Please help with Tahoe porpoising

My brother picked up the new prop today and it totally fixed his problem. We were both surprised at how good the boat rode. It took down his top speed, but it improved his hole shot. He can now trim up his motor without bouncing us out of the water. Thanks everyone for the replies. Jeremy

 

[Maclin]

Re: Please help with Tahoe porpoising

Good deal

 

[DuckHunterJon]

Re: Please help with Tahoe porpoising

I stand corrected - good to hear you got it fixed. Just curious what your brother went from and to in prop size/pitch. Thanks.