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K D Perkasa - design detail

Exhaust design

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Brian Porter 231/07/2021 15:26:20
24 forum posts

Hi, can anyone please tell me from which part exactly did the exhaust smoke exit please? We’re including a smoke generator & are uncertain.

There’s a bulbuls section where the two exhaust pipes meet & then a short vertical section above but we cannot discover exactly where the outlet is. We don’t want smoke coming out of the wrong bit!!



Ray Wood 231/07/2021 15:48:42
2547 forum posts
877 photos

Hi Brian,

The 3 Gas Turbine Jet engines exhaust from the transom of the boat, I doubt it there was much smoke from them just a a heat haze !! I'm sure there would a diesel generator on board to run the electrical systems when the main engines are not running in port, or an APU Auxilliary Power Unit as most airliners use on the ground when the main engines are not running.

Hope that helps.

Regards Ray

Edited By Ray Wood 2 on 31/07/2021 15:49:08

Brian Porter 231/07/2021 16:02:07
24 forum posts

Hi Ray, thanks for the input.

This getting very confusing as we’ve read the three large transom flaps (ours power open & close) were air intakes for the turbines. It certainly had a diesel engine as well for pottering about. The two exhaust structures each side seem big for just one diesel engine OR are they exhaust pipes as various sources suggest??

More help folks please!!!


Brian Porter 231/07/2021 16:23:14
24 forum posts

UPDATE. Have just found an old 1950s video that shows clearly & explains, the exhaust is on the transom as we originally thought & as Ray has said in this thread.

So, after further thought, given the speed of this boat I doubt hardly any smoke would have been visible in real life & difficult to see on our 93cm model so we’re probably ditching the smoke generator, saving both weight & battery life!


Ray Wood 231/07/2021 16:43:04
2547 forum posts
877 photos

Hi Brian,

The bonus of having the jet engine efflux thrust exiting the transom was an extra 550lbs of thrust per engine at maximum speed.

Most of the technical data is covered if your research HMS Brave Border development & design, The Perkasa's were an export model to other countries.

A friend of mine was Chief Engineer on HMS Sabre a slightly longer boat, and said he had an easy job

Regards Ray

Edited By Ray Wood 2 on 31/07/2021 16:45:45

Richard Simpson31/07/2021 16:52:15
766 forum posts
371 photos

Just thinking about it why would you want the air inlet to be saturated with sea water? Inlets are always high and, in this case, as you say the three flaps on the transom are exhausts.

John W E31/07/2021 17:12:37
276 forum posts
272 photos

transome.jpgjet drawing number 1.jpgHi there

Ok, I have made a quick web search as the book which I have has grown legs and disappeared. I only have the 'older' version of the book High-Speed Small Craft by Peter Du Cane and this chap was the chief designer of the Brave Class. The air intakes, if I remember rightly, were just back of the bridge - either side - facing aft. They look like companion ways. This is where the air for the jet engines is drawn from. As has already been explained the exhausts exit through the transom and there are diesel generator exhausts mounted on an inverted V-shaped mast on the aft superstructure. This sometime varied on different vessels.

Couple of pictures here ....


diesel exhaust.jpg


Edited By John W E on 31/07/2021 17:13:12

Brian Porter 231/07/2021 19:16:48
24 forum posts

Ray - back in 2002, when we bought this kit I got some blue prints from Vosper Thornycroft but they don’t cover everything, also I mistakenly asked them for the Brave Borderer rather than the Perkasa P150 which went to Malaysia. A major career changed meant we abandoned it halfway through, retirement have allowed me time to pick it up again so we (my son & I) stripped it back to a bare hull earlier this year.

Richard - we though of that so the design cunningly prevents water entry but allows the sound (original x3 gas turbines) out. We’ve got as close as possible to the original transom design. When we’ve finished I’ll post some pics and then likely learn what we’ve done wrong! Thanks & I appreciate your input.

John - thanks for that, I see now where the diesel exhaust exits but as I said we’ve ditched the idea as it’ll hardly been seen as that photo shows! Thanks for your help.

Regards to you all


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