external transom mounted fuel tanks

The big concern is to handling.. most boats that have transom or hull extensions need work done to the steering gear as the change in waterline length effects the rudder and its moment of effort. I believe the Hatteras extensions also move the rudders aft to keep steering effective.

HOLLYWOOD

Effectively a hull extension. Apart from the recommendations above to involve a NA (I agree with that) you are adding buoyancy. While this is partly balanced by the fuel (but not fully...lower density) as you burn fuel that ballasting effect will be progressively lost, your stern will ride higher and higher & you will become unstable, perhaps dangerously so in a following sea.

If the idea had any merit, NA's would have tried it long ago.

I can't speak for anyone else....but I do pretty much know what the issues are...just not how much because I haven't run the numbers.

But the issues (all but a few) are pretty clear and people are discussing them.

Many of the issues can be overcome but when all is said and done...is it really worth it for the space gained? Maybe the areas could be used for something else and space traded...but Mark is interested...well see just how much it's worth to HIM.

psneeld said:

I can't speak for anyone else....but I do pretty much know what the issues are...just not how much because I haven't run the numbers.

But the issues (all but a few) are pretty clear and people are discussing them.

Many of the issues can be overcome but when all is said and done...is it really worth it for the space gained? Maybe the areas could be used for something else and space traded...but Mark is interested...well see just how much it's worth to HIM.

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Yes, we know the issues, just not the extent of problems each might cause. My wording was poor. But it's definitely not like popping a unit on the back of a fishing boat for an outboard.

That's the great thing about our boats. They can be anything we want them to be. All modifications are not equal or well received by others, but at the end of the day the only person that has to be happy with it is the owner.

Mark seems a prudent owner and unlikely to make a rash call. Definitely thinking outside the box, not all that different from other thinkers.

CPseudonym said:

That's the great thing about our boats. They can be anything we want them to be. All modifications are not equal or well received by others, but at the end of the day the only person that has to be happy with it is the owner.

Mark seems a prudent owner and unlikely to make a rash call. Definitely thinking outside the box, not all that different from other thinkers.

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And very opposite from some, like me. I just prefer going with the vanilla, stock as built by manufacturer approach. The proven one. That's why I don't order custom boats either. Don't want to be the first and only, so go semi-custom with proven hulls and equipment. I admit then to being very conservative in this respect and having little risk tolerance.

It's really sort of humorous to find us conservative in respects like this when we're the opposite in other areas of our lives.

I'm sure Mark will figure out what he wants, and how to get it best done. I'd be an anxious wreck waiting for it to be completed and launched and see how it did. Just different people.

Where is Tad Roberts when we need him?

Analysis, conversation and discussion has run it's course and now it may be time for Mark to dump his questionable idea or start a build thread.

Yea a build thread Mark.

How about some preliminary drawings?

Show Hendo how it's done.

I`m seeing the insurance underwriter clerk read Mark`s disclosure letter of adding an underwater fuel tank bolted outside the transom. " Hey Fred, take a look at this!" "Wow" says Fred, "better show this to the boss", "Hey boss...he got a NA to sign off on it, but sheesh, I dunno...".
On the other hand, how is it different to oil tankers, basically cigar shaped metal buckets filled with crude oil? Two skins required I think.

hollywood8118 said:

The big concern is to handling.. most boats that have transom or hull extensions need work done to the steering gear as the change in waterline length effects the rudder and its moment of effort. I believe the Hatteras extensions also move the rudders aft to keep steering effective.

HOLLYWOOD

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A lot of boats get extended with no change to the location of the steering gear. Broward's come to mind. I ran a one that started at 85' and ended up 98'. While it's better if the gear is moved aft after the stretch, stretched boats that the steering gear has not been moved do handle a bit differently after there stretched but it's nothing you can't learn to compensate for.

Mark, maybe she could look a little like a Menorquin. We have already had a discussion on that design. I hope this post doesn't rekindle the Menorquin haters here.

Capt.Bill11 said:

A lot of boats get extended with no change to the location of the steering gear. Broward's come to mind.

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I've spent time on a Broward with a hull extension. It did not have the rudders moved aft with handling in following seas an issue. But a Broward vs Mark's vessel are two different animals. The Nordhavn 55 was successfully stretched to a 60 with rudder moved 18" aft as I recall. Twisted would know for sure.

Mark's vessel could be made into a single engine, a proper FRP extension done and about 2/3 of the current fuel capacity built in with integral FRP hull tanks. Range would be about 700 miles with a reman 220 HP Cummins 6. About 3,500 pounds of ballast would would be required to compensate for the the removed iron. This would be a really great vessel for the open water especially with the addition of active stabilizers. Art's legacy designers in San Diego could pen this up in no time. And the extra cockpit and deck space could be used for many purposes. Now we're talking!

Mark: I think you're a provocateer extraordinaire. The next thing you'll be telling us is that you're anchoring out in NY harbor in a hurricane!

Provocative though it may be, I don't see why it wouldn't work just fine, but with the time and materials involved to do it well, and the doubts you'd create on resale, I'd think you'd save by cutting holes in the hull or deck, doing the swap with plastic, and patching them back up again. I like the looks of your boat just the way it is.

Seriously, how large of an object could you get into the tank space if the current tanks were jig sawed into pieces. No doubt, this would be a lot of work, draining, rinsing, vacuuming, sawing....but there are guys that do that. A few years ago, I had someone saw my stainless holding tank into three pieces before I replaced it with plastic. Yeah, stainless. It was quite a few blades and it was in a terrible spot. Genset also had to be pulled.

sunchaser said:

I've spent time on a Broward with a hull extension. It did not have the rudders moved aft with handling in following seas an issue. But a Broward vs Mark's vessel are two different animals. The Nordhavn 55 was successfully stretched to a 60 with rudder moved 18" aft as I recall. Twisted would know for sure.

Mark's vessel could be made into a single engine, a proper FRP extension done and about 2/3 of the current fuel capacity built in with integral FRP hull tanks. Range would be about 700 miles with a reman 220 HP Cummins 6. About 3,500 pounds of ballast would would be required to compensate for the the removed iron. This would be a really great vessel for the open water especially with the addition of active stabilizers. Art's legacy designers in San Diego could pen this up in no time. And the extra cockpit and deck space could be used for many purposes. Now we're talking!

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Always been my dream! Some will remember I am very seriously considering conversion to a single and yes a canoe stern is the stuff fantasies are made of. 3' of extension for the considered tankage would not require any rudder changes.

Daddyo said:

Some more clarification:
I have not purposed doing this without NA approval (don't know how that got started). ............

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Because you didn't state that up front.

I beg your forgiveness, sorry.

An important thing I've learned along the way is; If you want the right answers, you have to ask the right questions.

Only if you are smart enough and what I have seen in TF...Holy cow...a bunch of weekend boaters think they can extrapolate beyond "filler'up" or should I save a few buck on this trip....gimme a break....and PS...inception into the bad boys club strictly prohibits posts like this....

Pui ?

Pui?.... english please.....

If that's "posting under the influence" I feel sorry for you and all the others that can't have a drink or two. Some of us are fine with it.

Even with a few...some of us are light years ahead of some here.

Don't enter a mental war you can't win.

Capt.Bill11 said:

A lot of boats get extended with no change to the location of the steering gear. Broward's come to mind. I ran a one that started at 85' and ended up 98'. While it's better if the gear is moved aft after the stretch, stretched boats that the steering gear has not been moved do handle a bit differently after there stretched but it's nothing you can't learn to compensate for.

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no doubt.. but in a Broward that size did they fill it with 20000lbs of fuel?

HOLLYWOOD

fryedaze said:

Mark, maybe she could look a little like a Menorquin. We have already had a discussion on that design. I hope this post doesn't rekindle the Menorquin haters here.

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Is the flat platform part of the boat or part of the dock?

Actually we filled it with 31,175 pounds of fuel. Why?

Capt.Bill11 said:

Actually we filled it with 31,175 pounds of fuel. Why?

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Adding 31,175 pounds of fuel to the stern (or bow or one side) of a boat will surely change the handling and waterline unless it's a very big boat.

More important is to remember that that 31,175 pounds of fuel will be reduced as the boat is operated and could reach a few hundred pounds before it is replaced. This means that the boat will never be consistent in its handling or attitude.

Fuel (or water) is best carried as near to the center of the boat as possible.

rwidman said:

Adding 31,175 pounds of fuel to the stern (or bow or one side) of a boat will surely change the handling and waterline unless it's a very big boat.

More important is to remember that that 31,175 pounds of fuel will be reduced as the boat is operated and could reach a few hundred pounds before it is replaced. This means that the boat will never be consistent in its handling or attitude.

Fuel (or water) is best carried as near to the center of the boat as possible.

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I'm not sure what your point is? The location of the fuel tank did not change in the stretch. The tank in a Broward is built into the hull approximately in the center running a bit aft as I recall. When they added the extension they built in an extra water tank. Can't recall the capacity.

The boat handled fine. You just had to compensate for the forward location of the rudders which changes the apparent pivot point. No big deal.

And no, you would never let it get to just a few hundred pounds. That would be under a 100 gallons which is for all intents and purposes below empty.

Capt.Bill11 said:

I'm not sure what your point is? ...........

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I'll try again:

Adding a lot of weight (with fuel) at the stern of a boat will make it stern heavy. Removing that weight by using the fuel will return the boat to its original balance.

Think back to when you were a child playing on a see saw. Put a heavy kid on one end and that end went down. Put a light kid on the same end and it went up, assuming the same kid on the other end. It's physics.

Now if your boat didn't exhibit this behavior, fine, I'm not trying to say it did. I'm just pointing out that the laws of physics would normally cause the stern of a boat to sag if you put that much weight there and return to the original balance when the weight was removed.

rwidman said:

I'll try again:

Adding a lot of weight (with fuel) at the stern of a boat will make it stern heavy. Removing that weight by using the fuel will return the boat to its original balance.

Think back to when you were a child playing on a see saw. Put a heavy kid on one end and that end went down. Put a light kid on the same end and it went up, assuming the same kid on the other end. It's physics.

Now if your boat didn't exhibit this behavior, fine, I'm not trying to say it did. I'm just pointing out that the laws of physics would normally cause the stern of a boat to sag if you put that much weight there and return to the original balance when the weight was removed.

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Yeah I get all that. What I didn't understand is why you quote me and then started talking about added fuel weight in the stern. As I stated and apparently have to restate, the boat I was referring to DID NOT have a fuel tank added to the stern. Just an extension. The fuel weight I quote was the same before and after the extension and it stayed in this same general location. So of course it didn't exhibit the same behavior as a boat might that had that weight in aft.

Get as many steel drums as you can fit. Go to a local boatbuilder and get some acetone drums, always steel, always super clean. Arrange straps to hold securely, even in a sea. Burn the drums down first. When empty, push overboard and shoot full of holes so it sinks. Do make sure it sinks, to be polite to other boaters.