B28 clam vents

[Yannis]

Is there any particular reason why the clam vents are where they are so that everyone destroys their little toes on them?
Is there any reason why another type of vent, like a louvered one, couldn't be placed on the vertical side (step) of the B28 engine room, facing aft?
This would mean that you get rid of all clam vents as well as all tubing that brings air down to the engines. The louvered ones can be positioned right where the engines’ air intakes are, so no more tubes needed. And deck is freed of toe destroyers.
Can you think of any negative reasons why I shouldn't do that change?
Thanx.

[Preston Burrows]

Yannis,

Your toe stubbing vents must be an added upgrade?

Far as I know our decks at the engine area came without vents per Bertram, excepting for the blower arrangement for those with gas engines [besides the hatches / deck seams provide more than adequate ventilation and irrigation for the engine area!]

[Preston Burrows]

And just to be clear the gas engine equipped B28's came with a clamshell vent for exhausting located on the exterior port side of the hull, just forward of the raised deck area and a few inches below the rub-rail.

[Yannis]

Preston,

I didn't know that those clam vents were added by someone...
I also have that port hull air intake to the blower and still have the blower, I told my mechanic to get rid of it and insisted in keeping it.
I know what I’ll do, I’ll get rid of the one clam per side still left on the gunwale (the other one I have already moved under the sides so they don't bother anymore) and I’ll get rid of the blower too. I might put two louvered vents on the engine step facing aft, in case the others are not enough. I’ll have to make sure there is no water splashing into the air filter and turbos when I rinse the deck, but this I’ll have time to rethink when time comes.
Thanks.

[Tony Meola]

Preston

I would have thought that all the boats built in the US or destined for sale in the US were built to Coast Guard requirements. That requirement means that some type of ventilation has to be installed. On 99.9 % of the inboard gas engine boats this would have put a clam shell vent on port and starboard facing forward. Usually placed right about where the pilaster to the bridge sits. Then the two more set more towards the stern, unless the boats were built for diesels.

The forward facing vents are to force air into the bilge area as the boat is running so that any fumes would be theoretically pushed out the two rear facing vents. There are other ways to do it but that seems to have been the standard in the marine industry.

Here is an interesting read.

https://newboatbuilders.com/pages/vent.html

As you will see about 3/4 of the way down, the ABYC recommendations spell out what most manufacturers follow.

Some of the earlier 31's (not sure on the 28) there was a forward facing cowling mounted on the pilaster right at the gunnel. For those years that was less of a toe kick.

Yannis to answer your question of why not, you have to make sure that water is in some way restricted from entering the venting. With that being said the forward facing cowl will take in water in bad weather and rough seas, but when it rains the water does not enter if the clam shell vent is attached to the gunnel properly.

[Preston Burrows]

Tony,

Bear in mind the age of the boats versus regs etc. enactment, no doubt your information is accurate but if you look at B28 photos of the '70's vintage you will see no engine compartment 'ventilation' in the form of vents,louvres etc. was included as a Bertram factory standard either in deck or on pilaster for their gas powered models aside from the blower vent I described in my earlier post. So far as I know even the '80's vintage gas powered B28's, up to and including the last model year [~1986-1989], saw no other Bertram O.E.M.ventilation.]

Conjecture on my part now....I would assume the reg. standard Bertram were working to was a 'sealed' compartment with the blower arrangement acting as the sole source of fume extraction / ventilation for their gas powered B28's?

[Amberjack]

Early on Amberjack had issues with soot buildup on the transom, more than I considered to be normal diesel behavior. The long time diesel mechanic who takes care of Amberjack's Yanmar 6LP's explained to me that modern diesels get their increased horsepower per cubic inch by forcing more fuel and air into the combustion chambers and that this is a finely calibrated function. Restricting air (or fuel) flow to the engines will put the mix out of balance and result in poor performance.

Captain Patrick felt that there was enough air leakage through the deck seams and bulkheads to supply the engines but it just didn't seem to be there for my boat so I installed a pair of Vetus SSV150 vents in the inboard sides of the engine boxes down low in the companionway. Soot buildup decreased by two thirds and I don't have to scrub the transom every time I'm out for more than a few hours.

My 315 hp engines use 776 cu ft per minute at WOT which requires about 115 sq in unrestricted ventilation. A link to a good article discussing diesel air ventilation is below.

https://www.powerandmotoryacht.com/main ... ngine-room

Yannis--Consider retaining the old gas engine room blowers. I removed the ducting that reached down into the bilge and use them to cool the engine boxes after a long run when the engines are shut down.

[Yannis]

Doug,

I have one blower with a duct. It is turned on automatically with the port engine. So, when engine is off, it is off too.
What’s the problem with cooling down the engines? When entering any port, you have to slow down anyway for at least 5 minutes, or so.
Also, by the time you drop anchor, get the ropes, maneuver etc, that’s easily another 10 minutes at idle. So, I understand, the engines are cooled down. But even if they were not cooled down, what could the problem be? Is there any reason the engines should be cooler than what I explained? Thanx.

[Carl]

Yannis,
The blower is meant to evacuate the engine compartment of gasoline vapors.
I like it to also cool the engine compartment a bit after a long run, pull out humidity. I was told here they do little for that...but if my heads in there working on something, it seems almost a little more bearable with blower on. Mind over matter who knows.

What really exchanges the air in the compartment is the big hunk of metal pulling in lots of air and sending it out the exhaust.

[Tony Meola]

Preston

Best I can do is a quick check of Chapmans. Looks blowers became mandatory in 1980. But it appears that every gas engine boat needed It also says that baots built prior to 1980was required to have at least two ventilation ducts fitted with Cowls for each engine and fuel compartments. The exception was made for fuel tank compartments that had electrical equipment that was ignition protected and fuel tanks vented to the outside. There is also a provision for air to carburetors. It goes on to talk about the flow of air to force fumes out of the bilge while underway or when the wind is blowing.

I am not sure how Bertram managed to not have the vents, but they must have found a way. Funny it only worked on the 28.

[Carl]

Tony-

My 31 has the rear facing clamshells and the intakes are up on the sides of the house just behind the side windows.
Its an overlapped panel with a big hole in the back connecting to a passageway into the motor box.

[Amberjack]

Doug,

I have one blower with a duct. It is turned on automatically with the port engine. So, when engine is off, it is off too.
What’s the problem with cooling down the engines? When entering any port, you have to slow down anyway for at least 5 minutes, or so.
Also, by the time you drop anchor, get the ropes, maneuver etc, that’s easily another 10 minutes at idle. So, I understand, the engines are cooled down. But even if they were not cooled down, what could the problem be? Is there any reason the engines should be cooler than what I explained? Thanx.

Yannis-I can only quote my brother, a professional yacht builder and has more practical marine experience than I will have in 10 lifetimes. Also my Yanmar mechanic expressed pretty much the same. Why? I'm not so sure except that after a long run everything in that engine compartment-- spare oil, spare coolant, extra engine parts, hot water heater are all hot! so it doesn't seem a bad idea to cool them down. Also, idling while anchoring means no natural air flow through the vents, none of the huge air exchange from the engine itself and reduced water flow through the exhaust system. These engines are happiest at cruise speed, not idling. So I can see some reasons it may be good advice. Anyway, I follow it.

[Tony Meola]

Tony-

My 31 has the rear facing clamshells and the intakes are up on the sides of the house just behind the side windows.
Its an overlapped panel with a big hole in the back connecting to a passageway into the motor box.

Carl

Yes that is it, for the early years. Wonder why they changed it. At least it eliminated the toe kicker. I think it went away around mid 60's.

[Carl]

I wouldn't know much about those "new" boats from the mid 60's...


But can think of a reason.

- Mold and tie in a large fiberglass panel with trim

Or

-Drill a hole and mount clamshell



Im thinking bean counters and deadlines to push product

[Preston Burrows]

Tony,

I can only think that with these boats being built in pre-OSHA / EPA 'big brother' times that all Bertram had to do was comply with whatever USCG regs at the time......or maybe not......original gas B28's were plumbed with copper fuel lines including the fuel vent which had no anti-siphon valve, just a healthy 'loop' to prevent back-flow...…………..my copper fuel lines lasted from 1976- 2004 when I replaced all with 'rubber' hoses etc!

[Preston Burrows]

Yannis,

On the engine heat side of things remember once shut off the engines will actually heat up as they 'radiate' residual heat after their running operation, with the cooling system no longer circulating that heat radiates through the engine block until its apex is reached and the engine starts to cool.

Withdrawal of that radiant heat is assisted by way of extraction [via clamshell ventilators, blowers etc.] which can help prevent the build up of condensation through humidity, with preventing condensation that could add to corrosion issues being the objective of the 'assisted' cool down.

[Yannis]

Preston,

I agree. Keep in mind though that our way of mooring requires a lot of time in slow or idle. i’d say around 15 minutes. Almost always.
Condensation and humidity are terms that we have to look up in a dictionary in Greece. In the summer.
In the winter nobody uses their boats.
Thanks for your explanations.

[Tony Meola]

Preston

I believe all the boats came through with the copper lines. I believe at the time, they were the same type of lines used in planes, and I believe that is how they pushed them. Our 75 had them until we went diesel.