Engine Vents

Seb · 07 June 2004, 19:35

Im still looking for a way of venting an engine box on a diesel RIB that is actually watertight...

So, as so many have been to RIBex, i was wondering if anybody had noticed any clever (but actually simple) methods of doing this?

If so, i would appreciate it if someone could explain or post a picture.

Are water ingress proof vents available or am i just wanting the impossible?

I see that some diesel RIBs dont seem to even have vents. Are they actually necessary?

Louver vents seem to be the most popular...anyone had any experience with their effectiveness in big seas where spray ingress and swamping is likely?

John Kennett · 07 June 2004, 21:14

I have seen some RIBs with the air intake built into the A-frame, although I'm not convinced that they really allowed enough air flow to be efficient.

Quote:

Originally Posted by Seb

I see that some diesel RIBs dont seem to even have vents. Are they actually necessary?

They must have some sort of vent or the engine won't run!

Quote:

Louver vents seem to be the most popular...anyone had any experience with their effectiveness in big seas where spray ingress and swamping is likely?

As long as they are sufficiently baffled they'll work fine. Some water may get into the engine box, but if it is diverted straight into the bilge and pumped out then it's not a big problem.

John

roohairy · 07 June 2004, 22:06

Hi Seb, emailed this to you but can now post it so here it is for anyone else!

There is an inner and outer drum with a flat plate on either side, flat plate has a hole in to allow air in or out with a cover over. The ones in the photo have a gauze as well as a flashback arrester. The ball (red) is just smaller than the hole in the plate and the distance between side plates,so if it floats it'll block the hole in the top of the inner drum (fitted with gasket, green) The bottom edge of the inner drum is exactly at the same level as the bottom of the hole in the side plates to allow water to drain out.

Grey is engine box / lid / deck, fetching pink / purple is louvred plate

First pic is steel vent as used on ships, 2nd is adapted for back of P22 enginebox. (Side elevation) All right So I've uploaded them the wrong way round...

roohairy · 07 June 2004, 22:13

On reflection, this is OTT isn't it?

MarkWildey · 08 June 2004, 06:51

If you have a Type 42 Destroyer they are fine

On a more serious note someone explained to me that the air flow should be sucked in rather than forced in. So the direction of the air intake should be pointing away from the boats direction.

Regards

Mark

Seb · 08 June 2004, 08:27

Thanks for that.....

Any of the manufacturers out there got a simple solution?

Cheers

MarkWildey · 08 June 2004, 08:44

Seb

It depends on your engine box and layup of the boat. Whatever you go for I would reccomend have the air intake above the water line and try to seal the engine box.

That way when you stuff the boat, and fill it up with water, you won't block off the air supply or drown the engine.

Cheers

Mark

Pete7 · 08 June 2004, 09:17

Seb, whats wrong with the standard Halmatic engine box vents ? couldn't think of anything simpler. However both Vetus and Volvo do a catalogue with vents that have a back plate to stop water entering.

Pete

jwalker · 08 June 2004, 11:32

Quote:

Originally Posted by MarkWildey

On a more serious note someone explained to me that the air flow should be sucked in rather than forced in. So the direction of the air intake should be pointing away from the boats direction.

Mark, would you like to explain that one?

Pete7 · 08 June 2004, 13:03

Presumably he is taking about some sort of ram air effect aka F1 race car, but don't think its going to make much difference to 2 tonnes of Pacific Rib @ 25 knots. The halmatic vents are reversable and one P22 at Ribex had them facing forward (Rib Juju).

Pete

Seb · 08 June 2004, 13:17

In all the photos ive seen of MoD P22's, the vents face forwards. On my last one however, i had them the other way around as i felt they looked nicer and were less likely to suffer from water ingress.

The only reason im questioning vents in that on my 'intended' project P22 (that is yet to be confirmed), i want to change the engine box for a watertight one.

All of the boxes available for purchase which i have seen have louvre vents as standard and that is why i was questioning their effectiveness - i want to do as little modification as possible and thought that if somebody could confirm louvre reliability, i would stick with it.

Standarsd P22 vents seem to be the only good option now though as at least they afford good protection of the actual intake nozzle and are above the top of the tubes/swamp line. Shame they take up so much room!

Probably just being over cautious but thought that if im going to the bother of redoing th engine box, i may as well do the vents properly.

Cheers for the info guys

SEB

Seb · 08 June 2004, 13:58

Sorry Pete, while we on the subject of P22's again (although im sure that if im going to refurb one there is a long thread with 'stupid' questions and pictures etc looming), how does one tell if the hull is a Halmatic mould or a Victoria Marine mould....any ideas?

Am going to see one soon and would like to be able to identify what it is!

Whats yours? Any identifying features?

Cheers

MarkWildey · 08 June 2004, 15:25

JW

On Mike Garside's rib he has an air intake running up the cabin into a forward facing air intake on the roof. After a trip opening the engine lid showed a salt covered engine. Speaking to Alan Priddy, he told Mike to turn the air intake round to face away from the direction of the boat.

He did this and the salt disappeared.

From what I understood, from the conversation, the engine would suck the air in rather than having it forced in, along with the salt water.

As I know nothing about boats other than they have a pointy bit at one end does the above form any type of fact ?

Cheers

Mark

Pete7 · 08 June 2004, 15:49

Quote:

Originally Posted by Seb

Sorry Pete, while we on the subject of P22's again (although im sure that if im going to refurb one there is a long thread with 'stupid' questions and pictures etc looming), how does one tell if the hull is a Halmatic mould or a Victoria Marine mould....any ideas?

Am going to see one soon and would like to be able to identify what it is!

Whats yours? Any identifying features?

Cheers

Sorry haven't a clue, other than being very old with a thumbing great engine in it and a console that seems to get noticed everywhere.

Pete

jwalker · 09 June 2004, 00:23

Quote:

Originally Posted by MarkWildey

From what I understood, from the conversation, the engine would suck the air in rather than having it forced in, along with the salt water.

Mark, thanks for that. Yes, the water has more inertia than the air and won't be able to turn the corner. It's just a pity it also reduces the pressure in the engine compartment.

--------------------

Seb, I've seen the result of a hydraulic lock because an engine cover used the stainless type louvres and a wave went through and down the air intake. The little end eye and the big end eye were touching. Absolutely huge forces to bend the conrod double. It didn't crack though. Yanmar.

Scary Des · 09 June 2004, 09:03

Quote:

Originally Posted by Seb

Sorry Pete, while we on the subject of P22's again (although im sure that if im going to refurb one there is a long thread with 'stupid' questions and pictures etc looming), how does one tell if the hull is a Halmatic mould or a Victoria Marine mould....any ideas?

Am going to see one soon and would like to be able to identify what it is!

Whats yours? Any identifying features?

Cheers

Seb
If it’s got the original engine talk to Mermaid and they can tell you who they sold it to. Des

Scary Des · 09 June 2004, 10:10

Quote:

Originally Posted by Pete7

Presumably he is taking about some sort of ram air effect aka F1 race car, but don't think its going to make much difference to 2 tonnes of Pacific Rib @ 25 knots. The halmatic vents are reversable and one P22 at Ribex had them facing forward (Rib Juju).

Pete

Pete

Most P22 have forward facing vents, even the one on the VT web site.

I think that this is right because the vents point forwards into a narrow gap between the seats and behind the helm, any wave hitting from the front will be broken by the console and the helm and only light spray could enter the engine box. On my boat the vents have baffles that mean that any water going through the 2” gap at cover level then has to rise by 3” before it can enter the engine. This area between the seats is sheltered from the full force of the wind so there will be no ram air effect.

If you got a big wave from behind there is far less to stop the wave entering the vents.

Additionally my engine cover has a port hole that is put there to check for fire before opening the cover, with the cover one way round it’s over the pump the other way round (with the vents forward) it is over the turbo which I feel is the most like place to look for a fire.

These engines are water proof (allegeable) up to the height of the air inlet so the engine box can take a lot of water before things go wrong.

Des

Pete7 · 09 June 2004, 10:19

Des hi, missed you at the show, sorry wanted to meet and say hi. Totally agree, think my vents had to go on facing backwards because I cut the S/S handrail down and facing forwards they wont' fit or cover the vents properly.

Hope I don't get a green wave that high up the engine box or the crew will be in real trouble.

Pete

Scary Des · 09 June 2004, 10:39

Pete

Yes, I hoped to meet to exchange beer, chat etc but I had to work

. One thing I did get to see at the show was a part red P22 parked at the town quay that had a split engine cover that was hinges forwards and backwards.

It was a neat modification which I’m thinking about doing.

Des

Pete7 · 09 June 2004, 11:07

Thats a good idea, because with the seats fitted I can barely lift mine. Should be able to turn that modification into 25 pages of posts just for the Jackeens and Garf

There was a red tubed one in Lymington a while back that had a new GRP engine box in one piece so someone has made a mould for them.

Pete