Tomcat fuel fill / fuel vent upgrade?

[john8lyons]

HI All,

I have at 2008 Tomcat with two independent 75 gallon tanks port and starboard. The original fuel tank vents are high on the side of the gunnel, so high in fact that there is no room for the typical upward sweep that would keep water from running right down into the tanks. https://drive.google.com/file/d/1K-CHUcNVpoulpDGw9rmDDvPQ0_wm3jJx/view?usp=sharing

This poor design has been noted by others (e.g. Sunbeam's excellent http://www.c-brats.com/viewtopic.php?t=19284&postdays=0&postorder=asc&start=30) and it seems like the two best options to fix this are either: 1) try to fit an Attwood P-trap type vent into the original vent location https://drive.google.com/file/d/1OlxVWQLOS9euahf12jU19AzvI4x8vnAn/view?usp=sharing

or 2) abandon the old vent and switch to a combined fill / vent or what is referred to as a 'pressurized system deck fill'
https://drive.google.com/file/d/1NJyMLVyC5j2pFJs2bAEV3J5nAGNFikgh/view?usp=sharing

I like the idea of removing the vent from the side of the boat since it seems like it may allow rain or seawater to flow into the fuel tanks under certain conditions. However, I do worry a bit about the combined fill / vent caps given the location of the fill on the Tomcat's gunnel. Mine is located right by the step up onto the gunnel and might get walked on occasionally as me or others are moving around the side of the boat.

I'm also thinking about adding a Racor LG100 https://www.parker.com/content/dam/Parker-com/Literature/Racor/Racor_Fuel_Filtration_-_LifeGuard_Fuel-Air-Separators_-_RSL0184.pdf to prevent the seemingly inevitable fuel spillage out the vents when filling up, and during thermal expansion that seems to plague me here in Alaska after filling up for winter storage. What's unclear is whether the LG100 would work with a fuel fill cap vent. My guess is that it would but I wrote to Parker/Racor just to be sure.

Any thoughts on the best way forward or experience with any combination of these products? Things are slowly starting to warm up, or at least the daylight is coming back, and it has got my itching to work on the boat to be ready for spring!

-John

[Robert H. Wilkinson]

Not sure if it would be a good solution for your boat but you could look into converting it to a VOPR type fill. It would do away with the traditional open air vent - which cuts down on condensation in the tanks. It would involve replacing the fill neck and cap + rerouting the vent hose. It is designed to keep the tank at a neutral pressure - only allowing air in when there is a vacuum and air out if the tank comes under pressure(when gas in tank is heated up).

I have 2 pictures in my album here - http://www.c-brats.com/modules.php?set_albumName=album1611&id=IMG_1471_1&op=modload&name=gallery&file=index&include=view_photo.php

http://www.c-brats.com/modules.php?set_albumName=album1611&id=IMG_1472_1&op=modload&name=gallery&file=index&include=view_photo.php

Regards,

Rob

On edit looks like I am talking about the same one you linked here -https://drive.google.com/file/d/1NJyMLVyC5j2pFJs2bAEV3J5nAGNFikgh/view?usp=sharing

[john8lyons]

Hi Rob,

I think I'm going to have to go the VOPR type fill route. I purchased a couple of the Attwood P-trap style vents but the original vent holes are so high that there isn't going to be enough room below the gunnel to install them correctly. Seriously bad craftsmanship by the builder to locate vents in such a way that water can go directly in the tanks. Makes me wonder how much is in the bottom of mine...

I don't love the idea of the vent being flat on the gunnel since water could be pulled into the vent when the motors are running (putting a vacuum on the tanks) but it looks like this Perko model includes a 3/8" spacer to get the vents a little further away from water than might be on the gunnel. https://perko.com/catalog/fills_and_vents/170/vented_fill_for_1-1_2_hose_-_straight_neck/

Best,
John

[Robert H. Wilkinson]

John, sounds good. You could even add a second standoff ring to gain 3/4" height if you wanted. Not familiar with your boats fill location but I assume it won't be in a place where the extra height would pose a trip hazard stepping in or out over the gunwale. Just make sure if there is a horizontal run with the fill/vent hoses that you keep the vent line secured on top of the fill hose.

Regards,

Rob

[mstrpo]

I replaced one of the fuel vents on my 2006 tomcat as I had a side-impact on the fuel vent that required either fiberglass repair or a larger diameter fuel vent. I went with the Attwood and had drill out some of the gunnel from the inside to make room. The gunnel is plywood core and I painted over the exposed wood to help protect it. It wasn't fun or pretty (on the underside of the gunnel) but it worked.

[cmetzenberg]

perhaps i'm being overcautious, but i'm concerned about where the gas vapors go when that vent is moved. Those vapors are heavier than air and settle as low as they can, so having them outboard is good as it alleviates the possibility of those vapors settling in the cockpit...probably not a concern on a day with even a slight breeze.
I've never had any fuel water issues on my tomcat. Even when i change the fuel water separators i don't see any water in there.

[Robert H. Wilkinson]

Conrad, with a VOPR type vent system the vapours are contained within the tank untill pressure raises above neutral atmospheric pressure. This happens when temps rise as when the boat sits in the sun. Pressure is then released through the vents in the gas cap which is normally situated outboard of the cabin on the transom or gunwale. When cruising or when a sudden drop in temp. creates a negative pressure in tank air is allowed back in through these vents.

Regards,

Rob