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Old 08-30-2018, 12:44 PM   #1
Hpwatson
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Ballasting a Negatively Bouyant Gun?

Hi everyone,

I'm about to get going on a new gun build, probably a full-size blue water setup. I have some really nice Bois D'Arc wood from my family farm that I'm dying to use. It has a really beautiful color, bright golden yellow, and it's extremely strong. In fact, it's one of the hardest woods on the planet (janka hardness 2,620 lb-f). This, however, makes it a sinker. I've considered gluing it up with some more buoyant wood but I'd rather build it out of solid bois d'arc. Does anyone have any experience adding positive ballasting to a heavy gun? What are some techniques out there? I'm willing to give it a shot as sort of a pioneer if there's no tried and true method out there but hopefully somebody has some tips.

Thanks,
Henri
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Old 08-30-2018, 12:59 PM   #2
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Re: Ballasting a Negatively Bouyant Gun?

I've been wanting to build a gun out of a Bois D'Arc bow stave I have hanging around. I look forward to seeing how your gun turns out!
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Old 08-30-2018, 01:26 PM   #3
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Re: Ballasting a Negatively Bouyant Gun?

I checked the details and it's a dense heavy wood alright.

I was thinking about this recently... perhaps you could router a slot like for adding lead ballast but instead add high density builders foam - the blue construction insulation floats well. Then cap over with a wooden cover. The reverse of ballast but the same idea.
Or use some internal hidden laminates of a really floaty wood... western red cedar?
Just some ideas...
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Old 08-30-2018, 02:30 PM   #4
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Re: Ballasting a Negatively Bouyant Gun?

This is an interesting idea. As mentioned above, hidden laminates will be the easiest way to achieve this. Make sure the hidden inner wood is very straight and stable. Looking at the wood color, it would look amazing against teak or any darker wood in case you decide to alternate colors.
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Old 08-30-2018, 03:37 PM   #5
Hpwatson
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Re: Ballasting a Negatively Bouyant Gun?

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Originally Posted by portinfer View Post
I checked the details and it's a dense heavy wood alright.

I was thinking about this recently... perhaps you could router a slot like for adding lead ballast but instead add high density builders foam - the blue construction insulation floats well. Then cap over with a wooden cover. The reverse of ballast but the same idea.
Or use some internal hidden laminates of a really floaty wood... western red cedar?
Just some ideas...
Yeah I had the same thought, I think the wood is strong enough to overcome what would basically be an empty cavity filled with foam. Structurally I think it would be okay. Maybe I could even find a way to put an aluminum brace inside the empty cavity just to make sure it has support then fill with a HD foam. That or a hidden super buoyant wood is probably the answer.
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Old 08-30-2018, 03:39 PM   #6
Hpwatson
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Re: Ballasting a Negatively Bouyant Gun?

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Originally Posted by Nix View Post
This is an interesting idea. As mentioned above, hidden laminates will be the easiest way to achieve this. Make sure the hidden inner wood is very straight and stable. Looking at the wood color, it would look amazing against teak or any darker wood in case you decide to alternate colors.
Yeah if I can't figure out the positive ballasting thing I'll have to glue it with different wood, that will probably still look nice though.
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Old 08-30-2018, 04:33 PM   #7
Gary H
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Re: Ballasting a Negatively Bouyant Gun?

Air is lighter than foam … if you can figure out a way to incorporate a sealed enclosure without compromising integrity.

Grainger sells small aluminum tubing, maybe some thin-wall copper or PVC. You could easily experiment with different concepts by throwing them in the bathtub or pool to see how much floatation they provide.

Or another idea is to incorporate a sealed cavity or cavities directly into the stock. For example if you are laminating 1/2" x 2" pieces together, route a 1/2" section out of the middle of one of the middle laminates (before you glue it together). This would provide a 1/2" x 1/2" air void that could run almost the length of the gun.

Think about it …

edit: Don't know the prices, but these guys offer AL tubing in box sections as well as super thin-wall titanium round tube https://www.onlinemetals.com/
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Last edited by Gary H; 08-30-2018 at 04:57 PM.
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Old 08-30-2018, 06:39 PM   #8
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Re: Ballasting a Negatively Bouyant Gun?

I have built guns with a local wood called Tzalam with a similar S.G. The larger of the two (115cm)Is 1 5/8"X 1 11/16 and floats without the shaft. It is basically neutral with the shaft in. My 100cm gun of similar dimensions is a sinker. I think if you oversize the blank, then weigh the hardware,you can test it in a pool to see if you have enough meat to work with.
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Old 08-30-2018, 06:40 PM   #9
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Re: Ballasting a Negatively Bouyant Gun?

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Air is lighter than foam … if you can figure out a way to incorporate a sealed enclosure without compromising integrity.
What he said. Without being an expert I would route cavities along the outer laminates to add buoyancy.
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Old 08-30-2018, 11:40 PM   #10
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Re: Ballasting a Negatively Bouyant Gun?

Interesting.

Specific Gravity (Basic, 12% MC): .76, .86
Janka Hardness: 2,620 lbf (11,640 N)

When we talk about Wood Density for Spearguns, we are really talking about Specific Gravity as it relates to Water. .76-.86 is not sooooo bad. I've worked with Hardwoods such as Kwila/Merbau which are .68-.82. The Janka Hardness of 2620 is crazy. That is going to be a pain in the ass to sand and shape and cut and mill. But once it's done, it will be nice. I looked at the Dimensional Stabilty and the reports were not bad. The numbers aren't that far off Teak or other woods I've worked with. So why don't we use this wood otherwise known as Osage Orange? I guess it's hard to come by.

If you are making a 'Full Sized Bluewater' gun, you might be in the clear. But it will need to be a big girl and have some volume. If she has some volume, you may still need to add Lead. Why not shape it down close to what you are looking for and make sure it's got some volume. Then dress her up and throw into the water and take it from there.

Another way would be to use the Center of the Gun from Osage Orange and keep the sides parallel and then add wings from a lighter wood like Teak if neccesary.

I have lightened up some heavy guns I've had in the past for personal use by mixing in a lighter wood (teak) or by using a divnicyll foam. But. The most ideal situation here is that you design a Volumous Bluewater gun. (But make it nice with shaping and curves.) and then you can have a floater with all hardware and then thin it down from there to where you don't need any lead, and then fine finish the gun.

Let us know how it goes. Very cool. Make sure you Cure the wood properly and bring MC down below 12% before making. Try to use atleast 4 lams.
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Old 08-31-2018, 02:32 AM   #11
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Re: Ballasting a Negatively Bouyant Gun?

Sounds like awesome timber for a build. my wood guns are all solid Vitex around 0.8 sp grav - similar to online references for average density of M pomifera. Makes for an indestructible gun, and that dense wood absorbs recoil like nothing else.

Does require significantly more volume than teak etc to retain nice light in the hand feel. and you do need to rationalise the amount of stainless muzzle hardware, minimise shaft overhang

But with an Abellan inspired shape - mine are a slightly flatter wider cuttlebone profile - they still track thru the water beautifully.

Pair the dense stock with a grit-coated recoil handle shaped for your hand, and you have a gun that can throw a big shaft through a very thick fish. a super manouverable platform that you wont hesitate to pull the trigger on a massive doggie or a blue marlin

Last edited by kavachi; 08-31-2018 at 04:06 AM.
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Old 08-31-2018, 08:52 AM   #12
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Re: Ballasting a Negatively Bouyant Gun?

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Originally Posted by peripatetic View Post
I have built guns with a local wood called Tzalam with a similar S.G. The larger of the two (115cm)Is 1 5/8"X 1 11/16 and floats without the shaft. It is basically neutral with the shaft in. My 100cm gun of similar dimensions is a sinker. I think if you oversize the blank, then weigh the hardware,you can test it in a pool to see if you have enough meat to work with.
That's cool so basically no ballasting required? That would be awesome
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Old 08-31-2018, 09:02 AM   #13
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Re: Ballasting a Negatively Bouyant Gun?

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Originally Posted by Behslayer View Post
Interesting.

Specific Gravity (Basic, 12% MC): .76, .86
Janka Hardness: 2,620 lbf (11,640 N)

...

So why don't we use this wood otherwise known as Osage Orange? I guess it's hard to come by.

Yeah it has always struck me as the perfect wood for a speargun but it is rare. It only grows in the southeast US and it grows really slowly. The trees are also prone to growing in crazy twists and bends with hollow cores so it's even harder to get a solid straight section you can work with. My brother and I found 2 naturally fallen bois d'arc trees on our land and spent a month getting them out of the woods. At almost 60lbs per cubic foot you can imagine what it was like hauling 2 entire trees out! Anyways I've got a garage full of boards now and I'm dying to put some to use.

Your other points are good, I will probably take that approach and start bulky, test buoyancy, trim, test again, etc. If it ended up heavy and needing a bit of flotation what I might try is drill-pressing a few 3/4" holes on the bottom along the length of the gun (depending on what volume of air is needed) then sealing it back off with a thin veneer & epoxy. That will avoid putting a large empty chamber in there somewhere and will hopefully preserve some strength.

Thanks for the advice.
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Old 08-31-2018, 09:09 AM   #14
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Re: Ballasting a Negatively Bouyant Gun?

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Originally Posted by kavachi View Post


But with an Abellan inspired shape - mine are a slightly flatter wider cuttlebone profile - they still track thru the water beautifully.
Yeah I went a bit bulky on the last gun I built and was surprised that it still tracked pretty well. For this one I want to emulate the Ace roller speargun shape - wide and thin. Looks awesome in my opinion .

(http://www.acespearguns.com.au/produ...d-handled-gun/)
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Old 08-31-2018, 10:28 PM   #15
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Re: Ballasting a Negatively Bouyant Gun?

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That's cool so basically no ballasting required? That would be awesome
cut board to size, route the track in, and rough shape it. then tape the shaft in correct overhang position, tape handle and any hardware in respective position. then test float it, make sure you're starting with enough volume to float your preferred shaft

Being able to progressively plane/sand down the stock til its just barely negative in the muzzle with preferred shaft in is the key.

my test tank is the ocean so no need to try and guess that little bit of extra float from the pool

Easiest mistake with dense wood is taking too much meat out of the muzzle.

pic attached of showing muzzle of solid Vitex stock, the only stainless is a length of wire drilled thru, forming wrap pin and attachment point. note minimal shaft overhang - does require a bit of relearning aim point, but thats gonna happen with anew gun anyways - allows to keep muzzle volume to a minimum

recommend tung oil [F&W Kitchen Timber Oil my fave] for solid wood - looks good, provides plenty of protection, and super easy to fix up/recoat, unlike epoxy

i have two of these, seen a LOT of rough use and extreme sun in small boats and no sign of warpage or damage
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