Fuel tank placement, planing cruiser

Hello everyone,

I have a 1989 Thompson 25 foot cabin cruiser. Currently I have two 30 gallon fuel saddle tanks in the bilge along with a 12 gallon (I believe, haven't measured since boat is in storage) sewage tank, 6 gallon hot water tank, two 12 volt batteries, and a small block V8 engine...lets just say it is cramped. After doing some poking around, I noticed the space under my aft cabin floor is a large void, I believe large enough to have a keel tank placed underneath between the stringers. I know the 23 foot model Thompson (225 Daytona) has the tank in this location and it is 60 gallons. I am curious to know is there any reason that these tanks cannot be consolidated into a keel tank? I know just about every new cruiser of similar size is running with a single keel tank, some boats of that vintage ran with a large single tank just forward of the engine as well. I would like to spread things out in the bilge with the possibly of adding a small generator. Also, with everything in the stern and the small Mercruiser alpha drive, if you put passengers in the back seats, this boat is a bear to get on plane. The water tank is 10 gallons and is in the bow. The only reason I can think of for the current tank placement is the boat tends to run a little bow down at top end (tabs up, drive trimmed up) so adding weight forward may cause a bow down condition. Saddle tanks are a pain with a vessel of this size since there really is no ballast so the boat tends to lean at the slip after running off of one tank all day (unless you switch tanks frequently, which means you have to open the hatch and flip the valve). To counteract the bow down condition at WOT, I was going to look at going with a counter rotating drive (Bravo III) which seems it would provide a little bit more fore/aft thrust making the boat a little more sensitive to trimming. Thoughts? Thanks for your input.

Jon

 

The only place to store volatile fuel in any boat is in an outboard well drained and ventilated overboard preferably in a fuel cell ( a sealed tank vented overboard).
Similar storage can be fitted elsewhere to give balance to boat. Fuel stored within the hull of a boat and ventilated within the hull is asking for trouble as history has shown. You can make a boat much safer if you put your mind to it.

One of the greatest feeling of a safe boat gave me all the pleasure of boating knowing my family was safe with safe fuel storage drained and vented overboard and a safe remote fuel system in a inboard motor set amid ship. Nothing in the hull related to the fuel system or reticulation. We could cook up and live aboard with safety. Because all boats are different there are no plans for this system.

 

If the boat is difficult to get on the plane fit some good sized trim tabs and learm how to use them !! they can and will save lots time and hard pushing to get out of the hole and on the plane . plus they can trim your hull as well . if you have a little more weight on one side than the other just trim one down a little to even the boat up to level .
Fuel tanks as is already said need lots air space around them and never seal up the compartment where the tank is but have a air flow trough if possible in any direction .
Petrol vapor is heavyer than air so finds the deepest part of any hull to sit and gradually build up . this is an exsplosive mix and just one small spark and you and your friends and the boat are history for ever more .
Fillers need to be on the outer deck outside the combing to drain spills over the side and away !!, vents need to be one foot above the max height of the actual filler and up on a cabinside facing down and a little aft in a natural air flow if the boat is moving or stationary , if at all possible .
Always double hose lip all and any hoses connected to the fuel tank and to the motor its best to get all you hoses crimped properly again double crimped . take nothing for granted and double check everything three times .

 

I disagree, gasoline can be stored below decks safely, but there are precautions all must take, which are well established.

At issue here are a few concerns. What does the new tank location do the the boat's trim? IS the current trim correct? What's the boat's MT-1" and PPI currently? I the getting on plane issue power related or trim?

The first thing I would do before any of these changes would be to completely empty the boat of everything that's not physically attached. I mean everything from cushions to anchors, empty every single locker and storage bin too. Then take her for a run with just a skipper, check trim setting, etc. Next place a full crew load on her and repeat. Next, place sand bags in the cockpit, over where the new tank will live and try the runs again.

I'll bet you have a bunch of stuff, you've forgotten was stowed aboard and she's dragging around a 1/2 a ton or more of gear, she really doesn't want too.

 

Besides safety, an important consideration is trim. Weight aft may affect trim and seakeeping. Nothing worse than a boat with weight in her ends.

Also consider the plumbing needed for the tank. Can you run this plumbing when you mount the new tank. ? 90 degree bends in fill pipes are bad.

Link for OEM fuel tanks. http://www.moellermarine.com/oem/fuel_tanks/

 

I agree 90degree bends are a pain and depending where ther are placed end up coughing back from a air lock in the fill pipe ! Smooth gentle curves and a fall all the way from the filler to the tank so no part of the filler hose has a dip down below the tank filler pipe . just make sure the vent pipe is up higher then the filler !! Its really all just planin common sense at the end of the day !

 

Just imagine the suffering and strife that would have been saved if the designers and users of boats installed a fail safe fuel system on petrol engines in boats from day one and it could easily have been done. Why build your self a bomb just because it is the traditional practice. www.shareaproject.com/pages/projectsThumbs,p,9.00.html

 

Just imagine the suffering and strife that would have been saved if designers and boat users installed a fail safe fuel system in petrol engine boats from day one.Why build a bomb if you don`t need too? www.shareaproject.com/pages/projectsThumbs,p,9,00.html
If that does not work try www.shareaproject.com search projects remote safe fuel system for boats.
Google remote safe fuel system for boats.

 

The extreme vast majority of fires and other gasoline related mishaps, are owner related, not designer. You can't design against every potential, boneheaded move, a skipper might muster himself into.

 

Like the guy and his fuel tank and battery in the same compartment !!!

 

How long is it since you checked your tank mountings and straps ???

The way tanks are mounted and how they are suported leaves a lot to be desired in a lot of cases . silly little brackets welded to the side and a long threaded bolt to tension it to what ever and no locknut !! thin rubber between the tank and the hull frames and nothing to stop it moving fore and aft .
Have even seen tanks stuffed in places hard against the hull bottom between frames and nothing between the hull glass and the tank !! What happens when the hull bottom wants to move up and down when you in rough water ???
Liquid moves constantly all the time and never stops . side to side , end to end and when it reachs a end there a lot of weight wanting to stop suddenly it wants to move the tank off its bed specially when the boat is hitting into a head sea and the faster you going the harder its hitting .
When was the last time you had a really good look at your mounted tanks ??Hold down straps and what between them and the actual tank ?? probably never !!

 

The more air you have around your fuel tanks the more oxygen there is so bigger the bang.
No air means no oxygen so no explosion.
Fear for safety is the biggest reason for not enjoying the boating experience so why not make it as safe as possible.
Watching an operator of a petrol or diesel power boat reaching for the ignition switch for a hot start up,and wondering whether the bilge pumps and gas detectors have done their job.If a gas detector signals you have trouble which would not have occurred if you had no fuel inside the hull of the boat and smelly diesel or gasoline fumes in the bilges.

 

Maybe it's different in NZ, but this just isn't the cause in the USA, where if it starts, it's time to go. Most folks (the extreme vast majority) haven't any issues at all. A very, very small percentage, usually driving very poorly maintained and modified craft have issues.

I agree some things could be employed, but I don't see a huge need for major revisions to the way manufactures are installing gas tanks and fuel delivery systems.

 

Google Images boats on fire.. to see how often it happens ...to someone else.
Or Google Images speed boat on fire. The Captain of the boat tried to start it after it died in the middle of the lake and it caught fire so he jumped ship. Perhaps the Insurance companies should make safe fuel storage on boats safer and compolsory so you can have cheaper insurance..if you have any at all.

 

What about the center of gravity? Isn't a keel tank for 350-650 lbs of fuel in a normal cruiser the best place to put the weight, low?