how thick is transom on late 80's prostar ?

About 1-1/4" thick. Contrary to common myth of an all-fiberglass and no-wood boat, there is a wood pallet in the transom which is covered by a light layer of cloth and resin. From all I have worked on, the thickness is as aforementioned.

One thing I can't figure is why would the 88 Prostar need a wake plate? Those boats have one of the nicest ski wakes of any.

I'd think you may be crossing the wake on the flat part of the ski. Change that technique to better and more aggressively edge across the wake. You'll never know the wake is there.

I just can't see the added value of a wake plate on a Prostar. Each to their own.

$0.02

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On skiability
I heard these were great ski boats, thats why I bought it... Of course not as good as the 91-94 version but still I thought it would be more than decent.
I have not skied behind another from this era, but the mid 00 malibus that i ski behind often are great in comparison.
This boat feels like its a tail rider on the water, and I suspect because of that its churning up a larger wake? I have wondered if there is water in the hull. I have tried different line lengths. its best at 28 off but still not great (34 mph).
I have been disappointed in skiing behind it and adding the wake plates seemed cheaper and easier than selling the boat or tearing it apart to check the foam. I am assembling the wake plate kit and will set it up old supra style with turnbuckles so its cheaper and easier to install, the tab came from ebay, I expect the whole project will be less than $150... I will update everyone when its complete. Thanks for the advice waterlogged. I appreciate your help. -jay

Also I should add that I am a decent skier. In the past I was a regular course skier. While post knee surgery I don't pull like I used to... The way my prostar skis now is/feels really subpar.

Makes sense. I was asking to learn...thank you for the insight. Best luck on installing.

While you are there (at the transom) if logistics allow, consider reinforcing or upgrading the platform mounting brackets.

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I'd just pop off one of the exhaust tips and measure it, also take the fuel tank out and inspect it.

There is no harm in adding additional reinforcement, use woven fibreglass rather than CSM so you can add strength and thickness rather than just thickness or strength (with more exotic materials)

If you know of one locally, I'd take the boat down to a weigh station and check the weight.

That era boat has a great wake normally (I had one, well... that hull with the previous years deck on it), next to nothing at 32+ irrespective of line length. Rock hard wake, but very small.

You could also try a 5gal water container under the bow

Its interesting that some people say they love skiing behind this era boat and that its top notch, just behind the 91-94 version. While some others complain about it. I wonder if the hulls could have been built that inconsistently? Of if the hulls that don't ski well also have the suspected water saturated foam?
From my reading, only a few people have added a wake plate to this era boat but they seemed happy with the results... of course the supras from this era came standard with their version of the wake plate, and didn't later year MC also use them to improve skiability? hmm not sure.
Anyway, I hope the plate fixes it up some, I really like the boat all otherwise. Like many on here, it had been my dream for years to own a master craft. So i would like to love skiing behind it as well. Thanks for the tips on the ski platform brackets.

The build quality was a major selling point in the 80's and 90's, from memory they used refurb/renew the hull/deck moulds every 10th boat or something like that to keep the surface quality, so presumably they put a similar effort into the actual construction.

mine was a UK boat, it had the 88 hull with an 86/87 deck (with the non profiled windscreen)

did master craft actually make boats in the UK ? so it was not a jet fighter style windshield?

Yup, until '88. Mine was one of the last, they'd sent the new prostar hull moulds but not the deck, so mine was the same shape as the rainbow deck. They marketed it as a Pro-Comp 190.

We got the benefit of the new powerslot hull with the space and simplicity of the old layout.

landing_frame-9 by landychris, on Flickr