Posts by Diving gecko

Quote from Peripatetic

Every piece of wood is different: That is why specific gravity is generally listed as a range rather than an exact value. Math can give you a good approximation, but perfect weight and, equally important, balance, are best achieved in the water

Which is why I proposed he measure a sample of the wood that he is using and not just rely on a list. With a ruler and a scale you can easily find pretty much the exact density of the wood you are using to make your gun out of. This should get you some quite usable results if you are far from a pool or ocean.

I guess you could do it like that. Just remember that you don't need all the weight in lead. Your spear and trigger and other metal parts should be subtracted from the lead mass.

For sea water, you should multiply your total mass of the neutral assembly (wood, lead, metal parts) by approximately 0.025-0.029 depending on salinity of your area and that should give your the amount of lead you need to add.

But why don't you do something else - and what I mentioned earlier?
Measure the weight and volume of your wood samples. That will give you the exact specific gravity of the wood you are using.
Then you measure the weight of your final shaped wooden gun (without metal parts) and divide it by the specific gravity and that will give you the volume of your gun. Let's say your volume is 1500cm3. Then add the volume of the spear. E.g. a 140cm, 7mm shaft would be around 54cm3.
You don't really have to take into account the rubbers as they are almost neutral (very slightly buoyant).
So, the volume of you gun and spear is (1500+54): 1554cm3.
In fresh water, the gun should weigh the same in grams to be neutral. So, your gun with a volume of 1554cm3 should weigh 1554 grams to be neutral.
For sea water, multiply by 1.025-1.029 and that will give you the total mass to make the gun neutral.

Eg. your 1554cm3 gun should weigh (1554cm3 x 1.025g/cm3): 1593g to be neutral in seawater (with a water density of 1.025g/cm3). If your water is very salty you might need more weight.

Finally, assemble your gun with all the parts and weigh it - add lead until you get to 1593g. Done.

(If you are mixing wood in your blanks, it might not be as easy as the above)

Yes, I agree with Pete. Pneumatics are overall just a more efficient design. Well, when we compare to traditional single banded guns and some double banded ones, at least.
But I am really hoping to finally do some proper tests on some of my airguns in a month or two on my next trip, hopefully throw a Pathos 100 in the mix, too. It would be great to finally have a better idea about how my guns shoot - I started on pneumatics and have only shot fellow spearos' band guns on occasion.

I'll try to list the reasons I consider them more efficient:

• Pneumatics have close to 100% "band stretch". Meaning, the piston will push on the shaft through the whole length of the barrel. Though, with a bit less force at the end but still with much more force than bands which go slack and do zero work for about 30% of the 'stroke'.
  

  
  

• Bands have to expand during the shoot and move forward - both carry some hydrodynamic penalties.
  

  
  

• Bands add recoil (on traditionally set up band guns). An airgun only have to move a 10g piston forward in addition to the spear plus they have a bit more mass than your regular 28mm pipe gun. So, all in all a pneumatic should have less recoil.
  

  
  

• The piston in an airgun suffers from friction, but in all likelihood much, much less so than bands moving along a gun (and through the water as mentioned above). The spear in a pneumatic has different kinds of friction acting on it vs. a rail or ET on a band gun. There's a bit where the spear glides through the muzzle and also through the slide ring for the shooting line. The biggest one could be the effort to tug loose from the friction fit of the piston as the piston stops it travel at the shock absorber at the end of the barrel - I don't know if it is a lot or a little.

Hopefully someone will some day really compare the best of recent band guns to pneumatics. There's room for improving the traditional pneumatic, too.
One thing I do wonder about is whether it is a potential issue and "energy robber" that the spear in an airgun is only suspended at the ends by the muzzle and piston - there is no rail supporting it. The spear could bulge and sink a little in the middle as it is just hanging in air (in the case of a dry barrel gun) or water in the barrel. So, during the shot, this slight banana shape will have to be straightened out on its way through the muzzle and I don't know if that can make the shaft unstable - or the opposite. A long overhang could help with this, but personally I have as little overhang as possible as I worry about the guns being nose heavy.

I am not sure, but 30m/sec sounds high for a band gun?
A ten year old pool test done by Russians (Ukranians?) showed two shorter vacuum muzzled guns to shoot at about 28m/sec. A hydro-pneumatic gun in the same test was measured at 41m/sec. The guns were all very short as they were mostly intended for river hunting.
I don't know if they are muzzle speeds or average speeds over the course of 2m as a 2m distance to target is listed, too.

Hi Pete,
With respect, thanks for the history lesson.

Sorry, I just can't agree with you this time but this thread was never the place for that discussion in the first place, so I apologize for contributing to take it there.

I am sure Santa will find good gifts for her sons. I, for one, wish I was 16/17 and saw a long, very narrow package trying to fit under the tree.
Happy holidays and cudos to the OP for seeking good answers to make sure her boys get amazing holiday gifts:-)

All best, as always,
David

Thanks so much, and I agree with Don - that finale really put a smile on my face:-)

Welcome Jordan!:-)

Beware that the Gara 2000, if they are even still made, are supposedly super stiff. I had the 3000LD which are softer. That helps a lot with surface swimming.

I do, personally, think that some of the cheaper plastic fins could be an option. I base that on a few freediving instructors beginning to carry them in the Philippines. The first one, I know who did, is also a very good spearo (not that it matters much) and he said he was incredibly surprised about the performance of them. He said they were pretty snappy - which is often not said about anything other than fiber fins. I trust that guy's opinion on the matter a lot as he has never pushed a sale, quite the contrary.
I think he used to sell them at about 100 bucks. Mundo something was the name. Aquamundo, I think. I don't know if they were locally made or whether they came out of a factory in China under many different brand names.

Quote from popgun pete

Have you ever used a Riffe speargun, or owned any Riffe gear?

Short answer: Yes and no.

Long answer is that my point was two-fold.
The first was that a USD 400 polespear can not be said to be a budget option. No one could or should disagree with that.

The second and more tongue in cheek point people are of course totally allowed to disagree with.
Allow me to elaborate: I do find Riffe as a brand somewhat over valued and sometimes over priced. Same as I do Omer these days. Riffe guns, IMHO, has a place with people who would like a wood gun that is cheaper than a custom and aren't particularly worried about maxing out performance. I have shot fellow spearos' Riffe guns enough times to say nothing really impressed me about them. Maybe it is true that they are sturdy and will last a life time, though.

I might have been a bit too critical about the pricing on the Riffe polespear. I have, in other places, argued that products made in the 1st world do need to cost more and maybe a Riffe carbon polespear does need to be priced like it is. I honestly don't know and at the end of the day, anyone is free to charge whatever they want. Coincidentally, I am about to plunk down close to a month's salary on a new Mac high end laptop. While the pricing frustrates me, I am def guilty of being a (lazy, ignorant) fan boy sometimes myself.

I don't know anywhere near the history of our sport like you do and I should possibly have more respect for Mr. Riffe and his accomplishments and impact on the sport. But you know me Pete. I like efficiency in design and performance. Yes, I know tons of huge fish have been taken on their floats and float lines. I just sometimes wonder if there has been a bit of a lemmings syndrome in reg. to that brand.

If by three prong we are talking paralyzers, then I think it depends on how you define "decent size". I see a lot 3-5 pounders taken on paralyzers. I see even bigger ones. Obviously, spearos tend to talk less about the fish they loose, but I was surprised myself to see how well a good paralyzer actually works. Especially on a reef in conjunction with a beefy pole so you can jam the fish against a rock while it is still groggy.

That said, while I did order a paralyzer for experimentation for my own build I do expect to have a slip tip on my spear the majority for the time - I am going for a lighter carbon fiber design, so as Dan points out, the slip tip is a safer setup.

I humbly suggest we take the Riffe out of the equation. It's 400 USD for something not too short... But then again, it is a Riiiiiffe so obviously that name costs something, too...:laughing: Yes, it is carbon fiber, but that's not where you find the excess in price over other brands, I would argue.
It seems like Linghunt and Crist can both be had for app. USD 220-240 for about 8' models (with flopper tip) and from what I repeatedly hear their customer service should, literally, be second to none, especially to the bigger commercial brands. Gatku is about 260 bucks. Still not "cheap", but all should be good options.

I really like Linghunt's idea of DIY building but would be nice with a bit of support - I wonder if there is a way to reach out to someone local who could help the boys with the build. That would be awesome. Like a guided building course. Could be a deal with a local machinist or someone from the local spearing club.

For commercial options, perhaps look into GatKu? Don't know if they are budget friendly enough, though. But maybe a sale will be on today?
I haven't tried them, but they do seem to be popular.

I think Linghunt (LingHunt Engineering Inc.) is on this forum as well. He is in the US and makes custom spears - maybe he has a budget option. Also, he would be great in guiding in terms of size and setup. From reading his posts on different forums, he is a standup guy who shares knowledge readily.
Aaron Crist is much the same (Crist Spears) though both may be too pricey?

Sorry, I couldn't be of more help - I am just setting out to build my own polespear these days.

Yup, go with closed heels.
Dan, I think open heels are common in scuba because they like their booties a whole lot (walking on shore or boat with tanks) and often don't swim any major distances.
That said, I love using freediving fins while on scuba - especially if there is current and I need to chase after fish for underwater photography/video. I am not a commercial spearo so I don't spear on tanks...;-).
BTW, I think you'll see more and more scuba folks on long fins in the years to come - and, sadly, more reef damage as a result...

Back to the OP. For budget fins, plastic fins are just fine. A lot of us had plastic for our first pair of fins and they are near indestructable. I have taken mine down to 100 feet, so in that sense, carbon is not really needed. What is more important is that the foot pocket fits the shape of the diver's foot (if it is too tight, you can get cramps) and that there is room for a thickness of sock adequate for the waters, they dive in. Others can help you on the latter. Maybe 3mm in Florida? Or 1.5mm?
Different brands have different shapes of foot pockets and often divers mix and match blades and foot pockets, but most plastic fins don't have detachable foot pockets, so with those, you really have to go for the brand of foot pockets, when you decide.

For how wide the pockets are, it's tricky as few people have tried all pockets. But here is a list I lifted from another dealer on another forum:
From widest to most narrow:
Omer, Picasso, Sporasub, Pathos, Beuchat and Cressi.
(Those were the ones he had tried on).

Adding in some more comments from other users to that list and it could look something like:
Wide to narrow: Immersion, Picasso, Dessault, Omer, Sporasub, Pathos, Beuchat and Cressi
(This is just a compilation of different divers' feelings, so not sure how accurate it can said to be. E.g. some call Omer normal, some call them wide. But I think, on this list, only Beuchat and Cressi are really narrow and the rest are normal to wide).

I have had Omer, Pathos and Cressi. I have quite flat and wide feet and the Cressis are indeed narrow. So much so that I cramped up. Then I had Omer Stingrays that I found much more comfortable and now, I have Pathos. You might think that Pathos are narrow according to their place on the above list but I think they are still quite wide as they fit me well.

Man, out of a movie chuck full of awesome lines you choose the right one.
"Bad Motherfokker" is way better than "Royale with Cheese"...;-)

Cudos, love it!

(haha, the forum bleeps out if you spell MFer the correct way...! Crazy shit)

Sorry for using metric, but it's not hard to get PVC up to 250mm diameter. 160mm even easier so getting the buoyancy is not an issue at all. Bear in mind that PVC is a heavy material so get the pipes with the thinnest wall thickness that you can. I checked it a year or so back when I thought of making a gun tube - it would easily have weighed 3-4kgs in about 140cm.

True, if you CAD your design with all the parts you can pretty easily get your total volume and then multiply that with the density of salt water and you will have a mass that your gun should have if you want it neutrally ballasted.
Now, balance is another thing and a tad harder to find in CAD.
You can still get the center of volume easily but to get the center of gravity you need to specify the density of all the different parts in your gun; wood, steel, rubber, etc.

Ideally, you would want the center of gravity aligned with the center of volume or buoyancy - then the gun would float level. You can also make it slightly nose heavy, some folks like that.

But remember, that while you can add your lead ballast in one spot to place the center of gravity where you want it, you can achieve the same center of gravity by dividing the lead with some in the front and some in the back. It seems most builders prefer this. Not only because it gives them more room to dial in the balance (nose up or down) but also because if you place weight at the extreme ends, the gun will have more inertia and should, in theory, resist muzzle flip more.

It wont work if you just use regular neoprene glue?
Perhaps put one layer on the nylon first and let it dry out. Just to have something better for the second, regular layer of glue to adhere to?
I have done that with neoprene to neoprene if it was a tear in an old suit and the surface was very porous.

The math is a bit off since, as Linghunt points out, Mosaad is not taking volume into account.

But Mosaad does actually have an estimated volume available to him by way of the weight of the shaped blank (2000g) and the specific gravity of 0.64g/cm3. I guess some woods' gravity can range a lot and I don't know if the 0.64g/cm3 is one Mosaad calculated himself from measuring his wood or took from a table of densities.

Anyways, if we assume that the 2 kg is the weight of the shaped blank and the 0.64g/cm3 is the correct density of the wood he is using, then the volume of his blank is (2000g / 0.64g/cm3) = 3125cm3.

The handle will add volume and the shaft and rubbers, too so the overall volume will be bigger.
The volume of two 16mm bands for a gun with 110 cm band stretch is about 270cm3 (using 340% stretch). Perhaps a handle is about 150cm3? (no idea, really). A 140cm, 7mm shaft would be around 54cm3.
If we use these figures, the total volume of the gun would be (3125+270+150+54cm3) = 3599cm3.

So, in freshwater, the whole gun should weigh about 3.6kg to be neutral.
But I found an old number for the density of sea water in Abu Dhabi and it said it was 1.029g/cm3. So, I guess, in theory, Mosaad's gun should be neutral in Abu Dhabi waters if it weighs around (3599cm3 x 1.029g/cm3) = 3703g. Let's call it 3.7kg;-).
No matter what, it sounds to me like a beefy gun for a euro?

Yeah, I had nothing better to do this morning:-)
Also, as always, my math may not be correct, haha.

[EDIT]
Obviously, I took the liberty of guessing he is making a two-banded 110cm gun but I can see now that he quotes his spear weight at 500g, which points to a larger gun. Anyways, I think the method in itself is sound and the volume numbers would not change much either way (just different bands and spear volumes).
But you can also just build the gun and ballast/balance it in the pool, like everyone else;-).

Quote from mosaad

If it 45 rock hardness i ll buy from him also ,some country you can get labor charge very low compared to usa ,so its cheaper to fabricate rather than import from outside ,by the way what the material used by rabitech or other african seller its quench tempered steel but which alloy ?

I am, sadly, fairly sure he is not going to start a production run of these or wants to deal with the hassle of shipping out of China:-(. He just makes a few for his friends a few times a year.
The "South African" shafts are known to be carbon steel but no idea which exactly it is. But there is an extra step in that process as they are also coated - as carbon steel corrodes much easier.

Haha, yeah - I guess it does sound simple cuz it sounds like the OP has access to all the tools and facilities needed:-)

I know an engineer in China who works in a power plant, I think. He makes spears in 17/4ph on a CNC lathe, welds them and then drops them in with other parts when they need heat treatment. Job done pretty much;-)
Still a bit crude design wise but they are straight and functional. I am thinking of having him make a few with smaller and more aft-placed fins.
Price is in upper 20s (USD) so affordable, too.

Yes, that's exactly how it is done.
You can laser cut the shark fins and place them further aft that most commercial options - giving you longer band stretch. I think Pathos and perhaps Dan's spears (judging from pics) are some of the ones with the fins placed the furthest back.
Not everyone heat treats the barbs supposedly, but you can do that, too.