TOPIC: Glasspar Seafair Sedan rebuild (with diesel)

High Everyone. First post after lurking on and off for a few years. Hope you don't mind a long story.

We had our Seafair Sedan for almost three decades. When my Dad first bought it in the late 90s, it was powered by a Johnson 65 Commercial. We soon found much rot in the floor and transom. By then we had fallen completely in love with the boat and went all in (rather Dad did. I was still a bit too young to safely wield an angle grinder but learned to fiberglass quickly). It was stripped down to the bare shell, then rebuilt without any wood. Coosaboard wasn't really available back then so we made do with fiberglass and Aluminum. It held up fairly well for the next 25 years. Unfortunately, I think all those photos are now lost.

The Johnson 65 was soon swapped to an Evinrude V4 90Hp and stayed with that configuration for about 20 years. When the first V4 developed low compression on one cylinder, we replaced it with another used one and kept going.

After many years boat started getting a little long in the tooth, with stress cracks forming on the front deck and the rear catwalk at the hull perimeter joint. The second Evinrude 90 was also starting to be temperamental, and parts get a little harder to find every year. Seeing how nice many Seafair Sedans were being restored online made me want to revisit, rather than let the boat go. Dad felt the same way. And as for power, the thought of a modern EFI 4-stroke was tempting, but knowing what salt water does to electronics made me hesitant.

This is where the project started: A full teardown, but without the need to cut open the floor. The top deck did have to be removed to properly repair the catwalks and foredeck. After repairing dozens of holes and cracks we added fiberglass hollow beams for strength. Similar supports were added to the cabin roof. Any coring was done with Coosaboard.

The transom was stripped down to the bare skin again, then rebuilt with three layers of 1/2" Coosaboard, plus joining layers of fiberglass in between. The transom height was increased to accommodate the Mercruiser outdrive. Final finishing was done with with a thinned gelcoat applied with HVLP spray. It turned out well, but will need a polish once all the work is done.

Mercruiser outdrive? Yes, that's what we decided on. It turns out Mercruiser offered a 1.7L turbo diesel, starting in the early 2000s. In north America, these were typically installed in the smaller bayliner 2052 trophy boats. They have mixed reviews because many end up overloaded and resulted in early failures from high EGT's (fastest way to kill a diesel). The trophies are rated at only 31 MPH top speed but they are also 3500lbs empty. Glasspar Sedans are about half that weight. I think you can see where I'm going with this. The total drive system tips the scales at 653lbs (engine and leg) empty. about twice the weight of the V4 it replaces. But with the weight shifted forward of the transom, the distribution isn't too bad.

The biggest problem right now is...how do I post photos? It seems the maximum file size is flagging anything I try to attach no matter how much I reduce the size. Does anyone have some suggestions?

Looks like photos are working so I'll carry on.

The boat isn't finished yet, but its close enough to start some shakedown runs. She's a bit tailheavy compared to before, but that was expected. The new fuel tank will going in the front to help balance things out. For now, we're running out of a jerry can.

Tried with, and without a wing on the leg. Seemed to make almost no difference. Top speed settled at 33mph without the wing. Not terrible, but not great. I was hoping for 40 MPH, based on all the research I did before going with this engine. 33 mph is the same top speed as with the Evinrude V4 2-stroke 90Hp.

Fast forward a couple days and I swapped the propeller from 15 x 17 to 14.25 x 19. Top speed increased to 37 MPH. Not too shabby but not quite 40.

Porpoising starts at anywhere other than the full bow down tilt position, so we might be looking for some trim tabs. The max engine speed is also still going above the peak HP RPM of 4400, even with more propeller pitch. So I'll be trying even more pitch on the prop. Pretty sure I can get the boat up to 40 MPH once everything is dialed in. The real goal is being able to plane below 3000 RPM for best fuel burn and range.

Gheee wiz! You've got that Glasspar looking good, that dark green came out really nice
How does it plane out with the weight in the back without the tank weight forward?

Bilge wrote: Gheee wiz! You've got that Glasspar looking good, that dark green came out really nice
How does it plane out with the weight in the back without the tank weight forward?

The color was a tossup between off the shelf green and blue. I couldn't decide on one, so I mixed a small batch of them together to see what the color looked like. We all loved it, so that's how I made a "custom" Gelcoat color. Should be easy to mix up in the future if we need to perform any repairs.

Some testing with temporary ballast allows the boat to rest, and plane out pretty well. Even with most of the ballast removed, it still planes ok, but porpoising can happen.

The real fun is getting the right prop on the boat. The prop that came with the leg got us to 33 mph, with a hole shot of only 4 seconds. The next prop took us to 37mph. And I might be able to get a little more out of it. My goal is to top out at 40mph, with a comfortable planing cruise below 3000rpm. Right now with prop#2, it will still plane at 18mph turning 2800RPM (prop#1 needed 3100 for minimum plane).

The performance curves for this engine show nearly 4x the fuel burn rate at 4200 RPM vs 2800. 4200 is where peak Hp. I'm hoping prop #3 will get it down to 2600 rpm.

I have to be careful because over-propping and overloading killed many of these in the smaller bayliner trophy boats. This is why I monitor Exhaust Gas Temperature, and turbo boost pressure. Similar idea to the diesel truck tuners.