snorkle intake

[kelson]

So I'm back with more overkill ideas for my SIB. I was pulling together parts for my trunk drain and my buddy points at the outboard intake and says "that is what is going to get us in trouble if we get over run by a wave." True. It would probably help if Capt. Dave wouldn't try to surf the zodiac when he drives. Snorkels for 4x4 trucks have an intake that separates out most rain water and primarily deals with flooding by height of placement. It would be nice to have my boat theoretically capable of taking a passing wave. Not like everything is water tight on the outboard, but a quick submersion shouldn't stop it unless the intakes flood. I'm considering a snorkle add on with some height and the rams facing forward so the water can possibly pass by without directly filling the intake. Not impervious, but better than the straight shot down my intake that is stock. Don't see how to easily install a one way valve on an intake so that it wouldn't tend to suck closed in operation. Any better ideas regarding the intake design? Staying out of areas with waves and lots of kelp isn't an option... I'm looking at replacement Safari Ram Intakes for trucks. Only intend to install snorkel when necessary.

[doggypaddle]

You may need to re-jet the carbs if a long tube is fitted, the extra air intake length will cause the engine to run a bit rich, or if its an EFI it may require a remap if the hose causes much of a restriction. convoluted hose causes a lot of turbulence in the air flow reducing the effective diameter, It may not be significant but its worth bearing in mind.
To be honest i thought outboards were relatively good at keeping surf out by the cover design??

[Poly]

if there is enough water over the engine to stop it - what do you think the chances are that you are still in your SIB?

[m chappelow]

i dont think you will have any problems with the odd large wave over the engine,most outboard covers will hold back a lot of water ,even the RNLI,s outboards only have a valve in the carb intake and exhaust leg in case of total capsize or inversion ,i once flipped a sib over in surf and it was suprizing how long the engine ran on for underwater before it cut out ..pre kill switch days ,regards mart

[doggypaddle]

Originally Posted by m chappelow

i dont think you will have any problems with the odd large wave over the engine,most outboard covers will hold back a lot of water ,even the RNLI,s outboards only have a valve in the carb intake and exhaust leg in case of total capsize or inversion ,i once flipped a sib over in surf and it was suprizing how long the engine ran on for underwater before it cut out ..pre kill switch days ,regards mart

I thought they were good at keeping the water out

[kelson]

I have seen outboards stop after being overtaken by a small wave where the boat remained upright. My Nissan does have a design limiting the intake of water. The air/water has to flow up and enter tubes that pass down through the cover. I am going to douse the cover (off the engine) with a big bucket of water and see just how effective this cover intake design is. If the cover was reversible I could just stick it on with the intake forward when doing foolish things. Gee Mart, swimming around with my sib and the motor still running... that would get my attention. Maybe my kill switch isn't such a pain after all?

[chewy]

I've got a 15hp ariner Marathon, on Lifeboat day we have a raft race which includes flour bombs etc.
My outboard was covered so I shot about 5 buckets of water over it, it continued running no problem, I didn't think out of it really.

Somethings wrong if one wave makes it cut out.

[prairie tuber]

I think you are looking for a solution to a problem that does not exist.

[kelson]

I'm convinced. I set up my cover on a stand and taped some plastic sheeting around the bottom edge. Doused the cover intake heavily with a 5 gallon bucket. Not that much water ended up inside the cover. The intake diverter design works pretty well. Was curious about whether the engine under power would suck much water into the case. Didn't want to tempt fate by dousing it under power, so I put the cover back on the engine, started it up and taped off the cover intake. The vacuum on the tape wasn't all that significant. I don't think it would suck much more water through. It did make it obvious where in the case I did not have much of a seal. Other than the leaks along the cover seam and such I found a seal that was oversize for my outboard to power tilt wire and the seal around my oil panel on top of the cover wasn't sealing well. So I'm going to put my effort into the small steps that will have the most impact. Thanks to all for the direction. Having a high battery placement, covered and high electrical connections, an elevated tank vent and fixing a couple of seals on my cover sounds like the best I can do.

[Ed the Duck]

Originally Posted by prairie tuber

I think you are looking for a solution to a problem that does not exist.

Prairie, I completely agree. Tape up the air intake and run the engine. The air held in the engine cover will keep the engine going for quite a while.

After several years of operating in surf, I havn't had an engine fail yet due to water ingress through the air intake and then into the carb. Even with the boat flooded to the top of the sponsons, and the air intake being occasionally submerged by passing waves, no water was drawn into the carb. Have a look at the zapcat website and see some outboard engines being pushed to the limit in big surf.

Engine failures I have experienced in surf have been due to;

1. fuel starvation (air vent on fuel tank shut to prevent water entering tank) - hence why flexible non vented tanks are good.
2. Fuel starvation (fuel line severed due to kit not being secured well enough)
3. Engine stalling at low revs when re-entering water off the back of a wave (back pressure on the exhaust?) This may also explain an outboard engine cutting out if being overtaken by small surf at slow speed(?)

Kelson, In your original post you anticipated that the air intake would cause problems if overrun by a wave. In my (repeated and painful) experience, being overrun by a sizable wave often leads to far worse problems- damage to boat and crew caused by being pitchpoled and then dumped on by a couple of tons of surf! SIBs don't surf very well.

My suggestion is that you do everything possible to ensure that you can outrun the waves or take them on the bow! Consider geting a sea anchor (I now use a 6ft military drouge parachute bought from a surplus store in california) and use it if the engine does fail.

Have fun in the surf!

Ed

[kelson]

Thank you for the benefit of your experience. I'm pretty good at running in between set waves. Particularly when running over shallow bars in mex I try to keep the boat right up on the back of the leading wave where there is more water depth and just follow it in. The nasty part is if you snag kelp, trap lines or old netting. Not much time to do anything but hold on as the following wave overtakes you. This is the reason I got rid of my doelfin and use smart tabs now. That sucker really caught kelp and would put me in bad situations more often. I didn't have much faith in the outboard cover intake design, but it sure did test out well.

[chewy]

Works well on the Mariners....