Fuel tank - mount how far forward in speedboat?

[Anthony]

Hi all,

Heres a good one for your collective thinking...

I have a 17' speedboat (Dateline Bounty) that I am restoring, which includes replacing the fuel tank (riddled with crevice corrosion). The original tank would be expensive to have replicated, so looking to replace it with a standard off the shelf plastic tank instead. The original tank is alot longer and thinner than any off the shelf designs, so the new tank would be half the length (and higher and wider). Tank size is approx 60l.

Anyway, so the crux of the question is, should the new tank be located so its center of gravity is the same as the original tank, or can I put as far forward as possible as the last one also extended right into the bow? It has a 3.0l mercruiser inboard, so there is quite a bit of weight in the back to balance it out.

HERE is a quick profile sketch (not to scale) showing the approx location of the previous tank. Ideally I would like to put the new one quite far forward, (so its footprint lenght would be equivelent to just the front half of the old tank) but dont want to mess up the balance of the boat. I am replacing all the internal structure of the boat and it needs to be shaped around the tank, so need to get it right at this stage, rather than be able to experiment.

Any experience / theory on this appreciated

Thanks Anthony

 

[pvb]

In theory...

Your proposal only moves the CoG of the tank about 400mm forward, and it's not a particularly big tank, so shouldn't upset the balance.

 

[duncan]

Re: In theory...

yep - 60l is not a lot relative to crew etc.

if you can match the cog's then all to the good - if you can't then a little forward isn't the end of the world.

 

[FrankieJ]

Its agood idea to put the weight forward if poss. as it helps to 'get on the plane'.
I had a Dateline Bounty Jet in the early eighties, terrific fun.

 

[Anthony]

I did wonder if it would actually help to get the weight far forward as I have found it helps in other boats if a little overloaded etc to move some people onto the bow whilst getting up onto plane, but wasnt sure if it was a good idea to have it fixed there. But as has been pointed out its only 50-60l max, and CoG of tank not being moved forward alot, so fingers crossed it will be alright!

I am looking forward to actually trying this boat, I have heard they were good boats but THIS was the condition I recently purchased it in (I am always a sucker for a good project!), have gutted it since back to bare hull inside, and await all the Mercruiser spares to arrive from US to service engine.

At least now I have the layout for the new fuel tank pretty much sorted I can get on with rebuilding the interior structure (if it ever stops raining....).

Thanks,

Anthony

 

[pvb]

Quite a project...

Having looked at the pics on your website, it does look like quite a project! But I'm sure you'll enjoy it and be rewarded by the results.

 

[MapisM]

Overall, I'd agree with previous recommendations.
But be aware that you'll probably experience more difference in the boat behaviour between a full and an empty tank, compared to a more centered position.

 

[duncan]

whilst it may help getting on the plane it can be positively dangerous to have significantly more weight forward than the designer intended at high speed - such generalisations need to be tempered...........it's exactly the same issue as outdrive installation and maximum trim in; great for the holeshot but potentially dangerous for certain hull shapes at high speed.

 

[moondancer]

Some Fletchers used to have the fuel tanks forward but it is not generally a good idea. Central and middle is better,under the floor.

An OCR boat I used to have had a water tank in the bow to trim the boat and it could be filled and drained by moving a lever. It made a huge difference to the handling and as Duncan says it can make the handling dangerous at high speeds when everything needs to come aft.

 

[Anthony]

Ah OK, looks like it would be best to keep the CoG of the new tank in the same place as the old one....

Many thanks! /forums/images/graemlins/smile.gif

Anthony