1978 with a serious Porpoising problem

[Theomedic]

It has never been hung

[Theomedic]

We were out tubing today with the kids and the boat doesn't plane out at any speed. Even at 20mph the bow is way up in the air with 4 adults in the front seats. I' beginning to think it may be the prop? I found a used prop from a 1979 Ski Supreme, does anyone know if it will fit my 1978 Mastercraft?

[Cloaked]

Originally Posted by Theomedic

We were out tubing today with the kids and the boat doesn't plane out at any speed. Even at 20mph the bow is way up in the air with 4 adults in the front seats. I' beginning to think it may be the prop? I found a used prop from a 1979 Ski Supreme, does anyone know if it will fit my 1978 Mastercraft?

It should as long a it is a 1" dia shaft with a keyed mounting configuration. The exception would be a 1-1/8" dia shaft (either the prop or your shaft) or if it is a splined configuration from the Supreme. I think they had the 1" dia keyed confiuration. Also it needs to be LH rotation, and I think the Supremes used the LH Ford engines.

I doubt the prop is the culprit here. You'd likely just not get low end or top end performance but I do not think a prop would cause porpoising.

I had a 79 that porpoised at 36 + MPH. Never got it to lay down. From the sound of your issue, this is an increasingly noticeable condition as time goes on with speed becoming less of a variable. Is it possible that you're gaining weight from a waterlogged basement in the foam that was installed underfloor? It happens. Even if you pull the rear-centered transom plug, there are still areas in the floor that can hold water and not have an accessable drain point. If you have a leak (maybe along where the deck and the hull are married), it can be deceiving unless you have experienced this issue in the past. I'm just throwing out a bone here, and nothing makes me think this other than I have seen it happen in one way or the other. You may have a combination of issues leading to this particular one.

.

.

[Cloaked]

Originally Posted by ricford

I would bet my bottom dollar on rotten stringers. I had a J craft, which doesn't use stringer, but the plywood floor acts as the stiffener, and when the floor rotted out it porpoised really bad. Once that was fixed the problem went away.

Along the same line that I was referring in the pervious post.

Theo, I'd say for all practical purposes of the boat, you'll need to pull the floor and look it over this winter, or sooner. It's a decent project but it seems like you need to at least eliminate that possibility, or fix anything you find along these lines. Once you're there, I'd plan on redoing the stringers and build it right all the way from the hull.

.

[madcityskier]

Might talk to Devils Lake Watersports it Boaters Choice in Brooklyn. They're not a MasterCraft dealer, but Damon is knowledgeable and will likely work with you to try to fix the problem.

[Theomedic]

A couple of requested pics, hope they load?

Here are direct links: I can't get images to load without errors?
http://i1066.photobucket.com/albums/...c/6917c771.jpg
http://i1066.photobucket.com/albums/...c/f9e1a713.jpg
http://i1066.photobucket.com/albums/...c/b12d3770.jpg
http://i1066.photobucket.com/albums/...c/8f589448.jpg
http://i1066.photobucket.com/albums/...c/b52b8227.jpg
http://i1066.photobucket.com/albums/...c/6cde6c5c.jpg

I will try to load them again.

[Theomedic]

Looks like it does have a leak, I believe it's where the swim platform attaches as it looks like previous owner tried to calk it with clear silicone. The bilge area was full after leaving boat in water overnight.

[Theomedic]

[Theomedic]

[/IMG]

[Theomedic]