Engine room vent glass over

[Mike36c]

I'm putting together the details concerning the repair of my Frances damaged 1977 36. While she's out I'm going to glass over the hull side windows and probably the engine vents too, pulling air from the cockpit instead. Does anyone have experience with this? The cockpit is factory original with no bait prep station or freezer. Mike

[rtrafford]

perhaps a fisherman's tale, however i've been told that improperly placed cockpit vents can struggle to pull air at speed, low pressure et al. food for thought.

on my 53c i've replaced and molded in custom vents as well as adding additional vents in the cockpit to maximize airflow.

the lines of the boat are dramatically enhanced by building side vents that are glassed in, smooth to the hull--perhaps a 1/2 inch radius-- instead of the awkward original variety.

it cost me a ton of money to do it, but the results are special.

[Gcombos]

I also had to make some recent decisions re vents on my 36c.
It seems the trend to vent through the cockpit has fallen off over the years as some issues have cropped up like additional cockpit noise, increased sooting of the engine room on diesel boats due to the "station wagon" effect and uneven engine room air circulation.
A call to Slane Marine would be very worthwhile. He has a very nice, very updated vent that blows the original out of the h2o.
I went with a pair of his, they look as good as they perform. He has lots of pic's as well as many other interesting options relating to your boat.
Good luck!

[Mike36c]

Thanks for the input, sooting never occurred to me, that would be a good way trash a fresh white engine room. I've seen the Slane vents, very nice but a little pricey, over $2K if I remember correctly. Are there any other aftermarket options that perform and look good?

[Genesis]

If you have SIDE exhausts, it should not be a problem.

If you have TRANSOM exhausts, it may be a serious problem.

I have side exhausts on my 45C, and have no sooting problems with the cockpit intakes.

[rtrafford]

slane is a big proponent of transom exhaust on a hatteras. he believes side exhaust leads to rapid and frequent doctor's office visits for your diesels.

i've built a set of side exhaust molds designed to be glassed into the hull which look spectacular. they are for a 53c, but can be shortened to fit your application.

you may have the molds on the cheap.

[jim rosenthal]

where they are, personally. I also think they work better there. As far as the engine room vents go, if you have not seen Tom's work you should, before you buy anything else. They are phenomenally well-made. If I wanted to change the vent shape, I would have used those.
The original vents can be made to look better by recessing the slats deeper into the shell (they also don't get cracked as easily should you get close to a piling etc) I also decreased the number by one, they look less busy that way, and also rearranged them so that all the slats face backwards. (originally one set faced forwards and the other set backwards, which may have been an effort to scoop air in. It did not scoop air, but it scooped salt water vapor in nicely) I also shortened the hoses which conduct the air down to the engine room.
There is a formula for how many square inches of air intake area you need to have to both provide combustion air and cool the motors. On a 36 convertible, I don't think there is enough room under the cockpit coaming where you would go into the engine room to get enough air in there. You would have to come towards the center of the boat and even then you would be hard put to have enough area.
There's another way to do this, also: the vents from the 76 and later boats have a simpler design which is more modern, one horizontal slat, I think. I think Tom may have taken some of those off boats he updated, or he may have some of the older style vertical ones as well. I had these off my boat when it was painted. They are somewhat crudely made, but sturdy, and not difficult to restore.

[rtrafford]

jim, well constructed vents are in the hand of the constructor. buy something off the shelf and it will likely resemble "made in korea" quality. buy something from slane or any other custom craftsman, and likely you'll get something worthy of placement on your mantle.

make it yourself (with a bit of experience, assistance or instruction) and it can be as well made, properly built, as anything anyone else is selling. fiberglass is a thing of patience, effort, and investment. the ingredients aren't cheap, and the outcome of the product doesn't need to be, either.

i can guarantee that nothing slane has built is of higher quality than what is going into my boat. i wouldn't have it any other way. the investment is too important, too steep.

on that note, slane has an excellent reputation.

[garyd]

I bought a pair of slane vents. If your going to completely glass them in, no fasteners, tell him and he won't drill holes. They worked out great. I'd recommend them anytime.

I had the front portholes glassed over turned out great. The yard was a little concerned. I explained it is much easier to do finishing work on compound curves that flat areas. They tackled it and were surprized how easy it was. Gives the boat a much cleaner look.

[rtrafford]

yes, i've done the same with mine. ports are gone, vents are glassed in. the lines are much, much more clean than the original version.

house is next...

[rtrafford]

here's the work in progress (http://www.thedrsoffice.com/boat/hat.htm)

[Genesis]

Here's the poop on various exhaust options....

1. Transom exhausts tend to cause station-wagoning. When the boat is out of the hole, the exhaust is coming out right in the low-pressure area at the transom. Some of it WILL come upward and inward. If you leave the salon door open when running, you better also have one of the forward deck hatches open, or your salon will pick up soot. If you have under-cockpit air intakes AND transom exhausts, guess what your engine room will get? Yep. However, transom exhausts don't typically have backpressure problems, because they are always in that low-pressure zone behind the boat - even at idle.

2. Side exhausts don't suffer from this problem. The problem they DO have is during the transition to plane. Planing boats "squat" a bit during this time; the Hatts are designed so that at low speed the exhausts are completely out of the water. If you look at the side exhausts while on plane, they're also completely out of the water. The problem is during the transition. If you "nail" the throttles, as the boat squats the exhaust backpressure rises exactly as the turbos try to come online - this can cause dead turbos among other things. The solution to this is to know the boat - don't nail the throttle from idle; instead, come up to 1200 RPM or so, allow speed to build so the slipstream gets going (which draws the exhaust OUT), then ease up into boost. If you do this you find that backpressure doesn't spike.

Another option for side exhausts is to put in a small deflector just forward of the exit. This creates a low-pressure zone during the transition and avoids the problem - but it leaves something sitting out there where you can damage it. The spray rails at the stern provide some protection against them being ripped off the boat if you go this route, but not a lot.

I've had no problems with the side exhausts in close to 1000 engine hours - but I know what their pitfalls are and how to avoid them.

I also have a clean transom at the end of the day, and no soot in my salon or engine room.

[jim rosenthal]

..some manufacturers are going to a combination exhaust where you have an underwater exhaust and also a side exhaust? I have seen these detailed in some magazine articles. I wonder if the transition-backpressure issue is what they are trying to manage.

[Genesis]

These designs are kind of "cute" and attempt to solve the backpressure problem in a rather interesting fashion.

The underwater part of the exhaust is in the underwater slipstream and is basically a "relief" port. As the boat is accelerated from idle, the water flowing across the underwater port draws out the exhaust. That port is not large enough though for the full output of the engines - but it IS large enough to permit the turbos to spool up without excessive backpressure.

Once the boat is out of the hole the side exhausts are uncovered and all is well.

Full underwater exhaust has its own set of engineering problems on inboards - its "de-rigeur" with I/Os and outboards, because you can go through the prop hub, which for moderate engine outputs works real well - that's a nice low-pressure area and helps scavenging. Unfortunately on inboards there is no good place to put something of the required size without disrupting the planing surface.

Side exhaust has significant advantages, including less of a surge chamber requirement to prevent back-flooding the engine if you take waves from the stern while backing down or drifting. The reduction or elimination of station-wagoning is another benefit not to be ignored.

Cockpit air intakes coupled with transom exhaust is a problem in that ingesting soot is a great way to trash engines, and transom exhaust virtually guarantees station-wagoning to some degree.

Side air intakes have their own problems too - unless you have a very good filter and airbox design you will get salt spray in the engine room, which will trash everything in there. This problem IS solveable if the intakes are engineered properly. Its not just a matter of the louvers - you need to engineer the entire air path into the engine room so that what you get is clean AIR, and that the salt spray that comes with it is removed and drained. If you look at how larger yachts handle this you'll find that they are quite elaborate in insuring that what ends up in the engine room is just the air, and not the salt spray.

As with most things on a boat, there is no free lunch or cheap way out if you want to do it right. Just closing up the cockpit air intakes and installing side intakes can create at least as serious a problem as it solves unless you also address the spray issue. One nice thing about the cockpit air intakes is that boats with them almost NEVER have salt corrosion problems in the engine room.

My 45C has side exhausts and cockpit air intakes. I've had zero trouble with this design and have close to 800 hours on my engines in the last three years - but I do know how to run the boat.

[rtrafford]

seems to me that there has been a manufacturer migration that has gone from transom exhaust to side exhaust and now to corner exhaust...

[Mike36c]

My friend has a Luhrs with corner exhaust and I don't see any advantages over standard transom exhaust, it still gets soot on the transom and exhaust smell (express boat) with the front windows closed. My boat has the factory transom exhaust and with all the other work I don't want to get involved in changing it just yet. I sent an e-mail info request to Slane concerning the vents, it seems the best way to go and should look nice with a new paint job!

[Walter Pereira]

About a half dozen years ago, I had a yard on Kent Island in the Chesapeake Awlgrip my 43 MY. After much discussion, we decided to go the side exhaust route. The yard did a fantastic design and faired them with a small forward "lip" to create a low pressure area. The result was great.... Absolutely NO soot anywhere. By the way, my only problem with the yard was that I specified EPOXY resins and they used Polyester (not as strong ) Price was reasonable... Walt

PS Since I never "nail" the trottles the turbo's never seemed to suffer pressure problems.

[rtrafford]

nailing the throttles...who does this? beware similar problems occur when you crash off a plane. need to draw back slowly, too.

[mwastraastraoilcom]

All good comments. For what its worth, I have side exhausts on my 52 convert. I always change speed up/down slowly anyway, but I have to say, there is never never any stinky old diesel smell at any speed with that boat. I had a 37 with transom exhausts, and it was awfull at any speed-it always smelled. I sea trialed a 60 hat sport fisher a few months ago with transom exhausts, and immediatly dropped the idea of buying it...stunk like heck. The whole family threatened to throw me over the side. Anyway, I just love my side exhausts..maybe just lucky on this particular boat, but its been great so far.

Mike

[rmaher]

This may prove ignorant, but surely someone has manufactured a retrofit elbow that would turn the exhaust out from the stern?!? Out Hatt has a swim platform that should mostly protect such an appendage!

Rob

[dereknkathy]

Hi. On your side exhaust note. Wellcraft Novas from the late '80s and Four Winns Liberators had chrome side exhausts that were angled back about 60 degrees. You could put them in the side and put 4" hoses on them facing straight aft. Maybe we should just put I/Os in these guys...

[Starman]

I do not remember the exact numbers our 892's need in air flow, but we are building our own custom air vent boxes.

The old opening size was 9X49

The new opening size is 14X70

Air flow, and circulation of that air in the ER is an area that commands attention if the engines are to perform properly .

[the kuz]

Mike36C, You have the same year 36C that we do. Do you have the open rectangular engine vents? If so I would leave them. They provided sufficient natural air flow/volume on the instrumented seatrial for my re-power (330 B series). Another plus is that they are easy to plug/up-plug in the winter (a single foam plug covered with canvas or oil cloth for each side) and also easier to keep clean. To me they look nicer than the louvered ones, but others may like something else. Regards, Bob K

[Mike53C]

Mike36C, I remembered that a few months ago there was a post about the intake area, I include it just in case you need it.


The Amount of intake Surface Area Required is given by the formula

Horsepower / 3.3 = Surface Area in Square Inches

Please note, this is per engine (if you use the Horsepower of 1 engine).

For an 8V71TI developing Max HP of 450 the surface area required = (approx) 136 Sq Inches (per engine).

The Series I - 45C's rectangular Vents provide 66 Square Inches (per side). Tom Slanes New Style Vents Provide 234 Square Inches (per side).

Consequently, if you have the original Hatteras Vents (at least on the Series I - 45's), in all liklihood you don't have enough air intake area to begin with. So doing anything that blocks off or restricts the intake area I would think would Not be a Good thing.

OldHatt45

Hope it helps
Miguel

[johngalt]

I'm putting together the details concerning the repair of my Frances damaged 1977 36. While she's out I'm going to glass over the hull side windows and probably the engine vents too, pulling air from the cockpit instead. Does anyone have experience with this? The cockpit is factory original with no bait prep station or freezer. Mike
Mike, the PO of my boat glassed over the front windows, most of the portholes and modernized/customized the engineroom air intakes.My pictures seem to be too large to upload to this message but if you look at the smaller ones in my profile you might get an idea of what the job looks like. Go to the members list /johngalt/ pictures . Bruce