Engine Clearance Standards

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AJ
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Engine Clearance Standards

Post by AJ »

Hello all,

My boat needs new steps because of the new inboard and I was wondering what the minimum recommended/required clearance is between the front and top of a diesel engine? It's a Beta 20 HP.

Thanks,

AJ
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Tim
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Post by Tim »

If you're looking for a regulatory or "official" guidance for clearances, there isn't any from ABYC, USC, or CFR.

In general, leave as much room as you can. In practice, removable panels at the front end of the engine tend to end up very close to the engine; I have often seen panel insulation carved out in an area to allow clearance for a belt pulley. While I think this is too close and would prefer a minimum of 1", the point is that there isn't any particular information to guide how close you build your enclosure. Make sure no hoses or wires rub on anything, and remember that the engine and anything connected to it moves when in operation.

I'm assuming that these new panels will be removable for future engine service, etc. Obviously (or maybe not obviously, judging from many manufacturers' engine room designs), any permanent panels need to allow adequate room for service access on that side of the engine.

This boat, which also has a Beta 20, shows pretty typical (if not ideal) clearance. The front panel, when installed, allows about an inch of clearance to the nearest point.

Image

Be sure to leave adequate clearance around your exhaust manifold and riser, as these get hotter than the other parts of the engine. Usually, the clearance isn't as much of an issue at the aft end, but obviously you don't want combustible material to be overly close to these parts. A few inches is commonplace.

Assuming your new enclosure will be removable for service, you can leave fairly minimal clearance in most areas--though as much room as you possibly can is best in my opinion. Practically speaking, figure on a few inches everywhere, and only reduce it if it's critical. Don't allow anything to touch the engine anywhere.

Also, be sure there's plenty of air space for your diesel to breathe. You don't want it to suffocate. Additional air space is also good around your alternator, so that it can cool efficiently.
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AJ
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Post by AJ »

Thanks for the info, Tim! Things might end up being a bit tight around the alternator since the engine is so assymetric in that respect. I really should get around to posting photos of the engine install in the Projects section!

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Post by AJ »

Okay, after spending this past weekend working on a cardboard mockup, I can ask a more specific question.

I'm trying to box a step over the front of the engine. The ideal location of the step would be in a location that clears the highest point of the engine by scant 2" for the first 7" of the engine (measured from the front of the pulleys back). This design also leaves about 2.5" to 3" in front of the engine.

I could probably raise the the step another inch and narrow the tread from its present 10" depth to reduce how far it protrudes over the engine.

Would either the 2" or 3" clearance over the top of that front portion of the engine be acceptable? Or a bad idea?

AJ
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Post by AJ »

A couple photos for perspective. The space itself:

Image

The 10" step would cover back to about the rearmost bolt in that grouping of 3 bolts (2 smaller and 1 big bolt) in the top center area:

Image

AJ
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Tim
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Post by Tim »

In general, what you're suggesting sounds fine. 2-3 inches clearance is common, and actually a lot better than in a lot of installations. Do your best to leave as much air space as you can around the alternator, but practically speaking this will do the trick; at least the overall engine room is large (meaning there's plenty of combustion and cooling air available regardless of where the front of the engine box is).

Any pictures of your cardboard mockups?
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Rachel
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Post by Rachel »

Hiya AJ,

I was just recently wondering how your boat was coming along. Good to see your progress!

Is that the new fuel tank I spy behind the engine? Nice! (Did I miss a thread on that? If not, I'd love to hear how that project went; I do remember when you were first posting your ideas, and mentioning how you had a tight space to fit because of the steeply raked and "forward" rudder post.)

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AJ
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Post by AJ »

Tim wrote:In general, what you're suggesting sounds fine. 2-3 inches clearance is common, and actually a lot better than in a lot of installations. Do your best to leave as much air space as you can around the alternator, but practically speaking this will do the trick; at least the overall engine room is large (meaning there's plenty of combustion and cooling air available regardless of where the front of the engine box is).

Any pictures of your cardboard mockups?
Thanks again, Tim. Here are some photos.

Pre-engine steps:

Image

Image

Mockup with folding bottom step down:

Image

Mockup with folding bottom step up:

Image

Image

Portion of engine covered by the middle step:

Image

Clearance above engine beneath the middle step:

Image

Engine uncovered:

Image

Engine covered:

Image

AJ
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Post by AJ »

Rachel wrote:Is that the new fuel tank I spy behind the engine? Nice! (Did I miss a thread on that? If not, I'd love to hear how that project went; I do remember when you were first posting your ideas, and mentioning how you had a tight space to fit because of the steeply raked and "forward" rudder post.)
Hi Rachel, yeah that's the new aluminum fuel tank. Not much to report about it other than it's smaller than I wanted. The final mockup was for a 19 gallon tank, identical to the one you see installed in all respects except with 2 additional inches on either side.

Since I really wanted to launch last summer (I've yet to see this boat float), I contracted the boatyard to do the engine install. I went down to discuss the fuel tank mockup, and they informed me that they needed to take 2" off it to make it fit. After thinking about it, I approved the alteration since it'd still leave 17 gallons and change.

When the tank was done, it was 4" shorter. Apparently, they meant to say 2" off both sides. I estimate the new tank will fill to 15.5 gallons. Unfortunately, there have been a number of miscommunications on this project.

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Post by Tim »

AJ,

Your clearances shown by the mockups seem to be pretty typical. Based on what I see, I don't see any particular issues. Leave the most clearance you can, of course, but I think that looks about normal. It's always a compromise, of course.
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Post by bcooke »

Unfortunately, there have been a number of miscommunications on this project.
Funny, I had similar issues. It must be a welder/fabricator thing.
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AJ
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Post by AJ »

Tim wrote:Your clearances shown by the mockups seem to be pretty typical. Based on what I see, I don't see any particular issues. Leave the most clearance you can, of course, but I think that looks about normal.
That's good to hear. I'll keep you posted on how it turns out!

AJ
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