Does a boat with an outboard need a blower?

[ziggy12369]

I just bought a 1989 Cris Craft with two johnson 110 in the back. I was wondering if my boat needed to have a blower for the gas fumes?

 

[rrhodes]

Re: Does a boat with an outboard need a blower?

I am going to Assume your fuel tanks are in the floor. If so they vent outside of the hull and I can't think of anywhere fumes would collect unless the fuel system was damaged. Short answer is no.

 

[zach103]

Re: Does a boat with an outboard need a blower?

i second rrhodes post.. if you have an inboard tank you should see a small vent next to where you fill the tank.. on the outside of the hull.. look like this http://shareaproject.com/slideImages/8481.jpg

 

[jay_merrill]

Re: Does a boat with an outboard need a blower?

The issue is not as simple as whether or not you have an inboard or an outboard. I suggest that you read the following thread - be sure to read it all, because there are some differing opinions.

http://forums.iboats.com/showthread.php?t=299613

 

[ziggy12369]

Re: Does a boat with an outboard need a blower?

Thank you guys for the advice i was really worried about this because someone had told me that i was riding on a gas bomb if i didn't have my gas tank properly ventilated.

 

[rrhodes]

Re: Does a boat with an outboard need a blower?

Key word there is ventilation. But you are riding on a gas bomb either way.

 

[Ike-110722]

Re: Does a boat with an outboard need a blower?

First the law. In the USA, Canada and the EU, if you have an inboard gasoline engine with a cranking motor (an electric starting motor) you must have powered ventilation; i.e. a blower. An outboard mounted outside does not qualify.

Also the law requires a space with a fuel tank and non-ignition protected electrical equipment to be ventilated. That means if you have any electrical stuff that can make a spark, in the same space as the fuel tank, then you have to ventilate that space. If the electrical stuff is ignition protected you don't have to ventilate. If there is no electrical stuff in there then you don't have to ventilate.

The above is not opinion, it is the law in the US, Canada and EU.

The means of ventilation can be natural or powered. Natural is just two holes, one an intake and the other an exhaust. The size of the holes depends on the size of the compartment. Which is which depends on whether the boat is moving, or if standing still or drifting, which way the wind is blowing. It really doesn't matter. Also, if you have 15 square inches of area open to the outside for every cubic foot of net compartment volume, the space is considered by the USCG and everbody else as open to the atmosphere.

Powered ventilation is a blower. If you have tanks and electrical stuff in there I would definitely go with powered. It is not required, but hey, it's your life we are talking about here. Make sure it is an ignition protected marine blower. You need to size the blower based on the size of the space. And you need to size the ducting for the exhaust blower the same way. see the following http://newboatbuilders.com/pages/vent.html About half way down the page is a link to a graph of airflow vs compartment volume. But read the page and you will learn all about ventilating boats.

Now practical matters. Gasoline is nasty stuff. Gas vapors go boom whenever there is a mixture between 14:1 and 7:1, and a source of ignition. That's also why carburetors work. If you can smell gas, assume you have a leak. You might not, but better safe than sorry. Your nose is the best fume detector there is. However, after about five minutes the nerves in your nose will get desensitized and you won't smell it anymore, so take care of it when you first smell it. The best way to detect a leak in the tank or your fuel lines is to have it pressure tested. Most marine repair shops can do this.

Any way, probably more than you wanted to know.

 

[Walkthru]

Re: Does a boat with an outboard need a blower?

The best way to detect a leak in the tank or your fuel lines is to have it pressure tested.

...or use a match.

JUST KIDDING!!!! I thought I would be witty on my first ever post.

Seriously, if you smell it...FIX IT!

 

[ziggy12369]

Re: Does a boat with an outboard need a blower?

lol alright guys i guess im going to pressure test the tank.

 

[sschefer]

Re: Does a boat with an outboard need a blower?

Peter's info answers the question. If it would make you feel more at ease go ahead. I did.

 

[Titanium48]

Re: Does a boat with an outboard need a blower?

Thank you guys for the advice i was really worried about this because someone had told me that i was riding on a gas bomb if i didn't have my gas tank properly ventilated.

Just to be clear about fuel tank vents and compartment vents:

A fuel tank should have a single, small vent (with a hose leading to the outside of the boat if the tank is not portable). This allows air in or out to keep the tank from pressurising on a hot day or collapsing under vacuum as your engine pumps fuel out. There should NOT be any air flow through the headspace of the tank. Gasoline tanks normally cannot explode because the headspace has too much gasoline vapor to burn. Active venting would prevent this and cause an explosion hazard, as well as wasting a lot of gasoline and causing hydrocarbon pollution.

A closed compartment containing a fuel tank, on the other hand, needs active flow through ventilation to keep the fuel vapour concentration below the explosive limit. This is particularly important with portable tanks, which are vented to their immediate surroundings rather than outside the boat. The usual solution on outboard powered boats with portable tanks is to keep them in an open area rather than a closed compartment.

 

[jay_merrill]

Re: Does a boat with an outboard need a blower?

Gasoline tanks normally cannot explode because the headspace has too much gasoline vapor to burn. Active venting would prevent this and cause an explosion hazard, as well as wasting a lot of gasoline and causing hydrocarbon pollution.

I'm not sure what you are trying to say here but if you are assuming that the liquid gasoline is what burns, you are incorrect. It is, in fact, the vapor that burns. This is also true of other materials. For example, when you light a piece of paper, it does not burn until the temperature of the paper has been raised to the point of vaporizing it.

As for explosions, it is the inability of the rapidly burning vapors, which expand at a very high rate, to escape the enclosed space (overpressure), that causes the problem.

 

[Titanium48]

Re: Does a boat with an outboard need a blower?

It is, in fact, the vapor that burns. This is also true of other materials.

Absolutely. However, the vapor will only burn if mixed with air in the correct proportions. For gasoline vapor, that is between about 1.5% and 7.5% by volume. If the vapor concentration exceeds that, there is not enough oxygen present to support combustion. In other words, there is too much gasoline vapor to burn. Choking an engine will make it stop running for the same reason. The vapor pressure of gasoline is high enough to produce a vapor concentration well above the upper explosive limit in the headspace of a fuel tank, provided there is no flow through venting.

 

[Ike-110722]

Re: Does a boat with an outboard need a blower?

Walkthru, joke taken as intended. Oddly enough when I was a little kid my older brother did just that. We had an old derelict car in the back yard. He decided to check to see if there was gas in tank by lighting a match. Fotunately there was just a small amount of fumes ,but the concussion knocked us all on our *** (uh.... the censor change my word to asterisks- how about keester). (me, my sister and two brothers) As you can tell, even though it was sixty years ago, I haven't forgotten it.

Yes the tank itself needs to be vented to the outside atmosphere. In a closed compartment there should be no vapors if there is no leak. The exception is cross-linked polyethylene tanks (hereafter called plastic) . Plastic tanks do permeate a trace amount of vapor. The boat manufacturer actually sizes the compartment so that the vapor concentration never enters the explosive zone. If done right there is no danger. The USCG has a rule about sizing the compartment based on the square footage of the tank's surface and the permeation rate. But it is best to ventilate. However, few boat manufacturers ventilate the tank compartment. They just close up the compartment.

By the way, when the EPA standards go into effect for permeation rates for fuel tanks, they will be so low this will no longer be an issue.