Trojan Boat Forum

You do need relief holes , Hear are 2 reasons you need them ,1) reduced back pressure when cranking .2 if the engine where to kick back it will greatly reduces the chance of sucking water back into the engine . ( I/O have flapper valves for this reason )

More relief hole examples... you don't need a huge (like 1") hole or anything like that - sometimes just a single quarter inch or so hole like this one (see the dot on the elbow) http://t2.gstatic.com/images?q=tbn:ANd9 ... qgApxvLLJ2 , or maybe a series of them like on this one http://www.marineparts.com/partspages/MUFFLERS/MUF1.HTM

A lot of older boats (ChrisCraft, Owens, Sheppards) from the 60's would have a rubberized plastic version of the first one that also has a streamlined or tapered shape to reduce drag. I have tried doing some searches but haven't found any good pics of one yet.

I don't believe a 1/4 relief hole would do the job . The The The Salsbury Hydrofoil has 6 hole shown on one side . If i made one I would go for a 3/4 to 1" hole or multi smaller ones

Have seen many apps with just a small 1/4 inch hole but I would think it depends on the power plant. Would also act as a siphon break.

1/4 hole won't do much if the engine kicks back ( spins back wards ). that would be my main concern . a rare occurrence but it happens .

I'm only saying what I have seen.

I have no relief holes in mine and have never had any back pressure related issues. The exit point is not that far below the water line therefore it doesn't create enough back pressure to be an issue. I kept this in mind when I made this thing and made sure that the exhaust dumped out no deeper than the relief holes on the gimbal housing of a typical MerCriuser I/O. Any further below the water line than this and I could see where it could become a problem.

rooferdave wrote:both my neighbours in my club have trojan 44's a 1976 and a 1980, the 76 has the exhaust pipes at the rear and are under water making his boat super quiet... could I do this?

Yes, my 79-F44, zero DB noise !!!!!!!!!!!!

FWIW, the Harry Schoell patented side exhausts really do work.

Muffler "boxes" are built into the hull liner.

Exhaust gasses exit the hull just below the waterline through a series of round openings.

The concept is sound, and there is no chance of "siphoning".

When I had the gassers the carbon monoxide detectors would sound ONLY if the sliding door was open and ONLY at the moment where she would climb on plane.

closing that door or opening a forward hatch would eliminate the alarm issue.

With the diesels, there is zero station wagon effect, UNLESS we are running with full eisenglass, and then, only at the point where we are getting up on plane.

The Schoell side exhaust feature was present on Internationals built with the vacuum hull liner.

The mid cabin based vessels have no liner and utilize conventional exhausts.

Didn't intend to hijack the thread, but wanted to share the info.

I don't understand why this concept has not been picked up by other builders.

RWS

RWS wrote:FWIW, the Harry Schoell patented side exhausts really do work.

Muffler "boxes" are built into the hull liner.

Exhaust gasses exit the hull just below the waterline through a series of round openings.

The concept is sound, and there is no chance of "siphoning".

When I had the gassers the carbon monoxide detectors would sound ONLY if the sliding door was open and ONLY at the moment where she would climb on plane.

closing that door or opening a forward hatch would eliminate the alarm issue.

With the diesels, there is zero station wagon effect, UNLESS we are running with full eisenglass, and then, only at the point where we are getting up on plane.

The Schoell side exhaust feature was present on Internationals built with the vacuum hull liner.

The mid cabin based vessels have no liner and utilize conventional exhausts.

Didn't intend to hijack the thread, but wanted to share the info.

I don't understand why this concept has not been picked up by other builders.

RWS

And yet another side note, Trojan used the old Bertram Velocijet concept on the 10.8 express in an attempt to rectify the station wagon effect..

It is my understanding that there was a great deal of "friction" between Schoell and Management.

Additionally there was the Royalty costs for the use of the design, which according to Management were somewhat "burdensome"

These are among the reasons they attempted to phase out the Schoell designs after the ten year run.

Trust me, that side exhaust really does work well.

RWS