Thinking Outside The (Mail) Box

[macblastr]

anyone ever consider using a jetski setup to blow holes? you can buy older jetskis for $500 and they range from 50-80hp, they have everything you need to get the water moving & you could easily route the water with pvc. Just a thought.

 

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[Salvor6]

Hey Brad,
don't buy a dredge. I have a Keene 6" dredge with a 8hp Honda engine you can use. It's been in storage for the last year. I have all the hoses too. It will move a mountain of sand! I'm gonna donate it to our group.

 

[stevemc]

Yes, I have thought of them(using a Jetski). Carl Fismer used one on the wreck of the Enracht? (spelling)a Dutch ship that is on the edge of the Intercoastal waterway in Ft Myers, and had tons of sand piled on it in the digging of the waterway. The bottom was 2-4 feet deep, and they needed to get down about 5 feet in the sand. They floated a Jetski with a PVC elbow on the jet outlet. It worked just OK.

 

[Monk]

ScubaFinder! To think outside the box! Would it be possable to rig up something to the back of a Jet Ski? Seems they kick out a lot of water. Be on that idea you'll have to use your mind to make something that will work.

 

[ScubaFinder]

For the original purpose of this discussion, that is almost a brilliant idea. A jet ski blowing from the surface would not be very effective...it takes a lot of water and thrust, believe me. Taking the motor OUT of a jet ski, and running it full blast pointed at the sand would be great. There is however, a problem with that. You could run a hose from the air intake on the carb to the surface, and the motor would run under water. But ther deeper you went, the harder it would be to pull air. Therefore the engine would run leaner as you went deeper, and at about 10 feet it would cease to run at all. Compressed air attached to the motor might work, you'd just have to retune the carb for the added resistance. Might be worth looking into, but I think just getting a boat is the smarter idea still. It is fun to kick ideas around though, thanks.

Jason

 

[ScubaDude]

Jason, I've got a diesel compressor that will blow 185 CFM @ 120 psi will that suffice?

 

[ScubaFinder]

Sounds like a built in turbo to me Brad, I got 20 bucks that says we can spin the piston right out of it! Wonder how big a hole she would blow before she blew up.

 

[stevemc]

Jason, the reason I bought (and then sold) a Jet Ski was to get right up on the shallow sand, next to the beach. But they sanded in the beaches there, and I just sold it to recoup as I didnt like riding them that much. Kind of dashed my hopes to work that area. It will blow the sand away in that way, but not in deeper water, and the jet is tight, not a big broad area like regular mailboxes do. I have seen one doing this. They put on a PVC elbow, by drilling 4 holes in the elbow and the aluminum jet outlet, and using 2 long bolts and nuts. Someone had to sit on it and just keep the throttle just right. Keeps the back end down too. I think for moving the sand in the very shallow water a suction dredge or something like a jetski will work, an air lift is too shallow in the shallow water. They need for the air to rise and expand to lift the sand out. And I dont think a hookah will move much air, maybe in deep water, with enough pipe up top, kind of like Petes scuba tank thingy. And yes, the usual airlifts use a large CFM compressor to make lots of air. They usually have huge compressors for that on the big rigs. A hookah is only 4 cfm or something like that. With a scuba tank anywhere from 77 cubic feet to 120-160 cubic feet, and you cant blast it out all at once, as Pete said it will last 20 minutes or something like that, is not many CFM.

 

[privateer]

the problem with mail boxes are while they due uncover a lot of surface area they also blow out and cover many smaller artifacts and they are limited to shallow water-with suction dredges you can empty the spoil into area that can be monitored by other divers-or if in shallow water sent to the surfaced and worked top side, the best bang for your buck i have found is the torpedo dpd-will run for 80-90 min per charge-blows huge holes and is pettry safe to use.

 

[ScubaDude]

Are you hinting toward the CFM of water moved, or something along those lines?

 

[ScubaFinder]

Well, in aerodynamics, we use the formula Prop Pitch X RPM = Pitch speed, this is how fast the aircraft would theoretically travel if it had no drag. Hydrodynamics work much the same, with the main exception being that water cannot be compressed. So your "pitch speed" would turn into the CFM of flow. Prop Diameter X Pitch would give you CFM based on how many RPM's you were turning.

In aircraft, a pitch of 7 means that (in the no drag theoretical world) you would move forward 7 units (usually inches in the U.S.) for each revolution. If someone can tell me how they derive the pitch number for a boat prop I bet I can figure it out.

Jason

 

[macblastr]

the amount of thrust a jetski puts out is enough to knock you off your feet from 20 feet away. I know from experience. I would like to see how the jetski performed that was used in this manner with the pvc. and at what depth? there would be no way to use the jetski underwater and control the pressure. I might mess with the idea this year. jetskis aplenty here in florida.

 

[ScubaFinder]

I'm with you Cornelius, your English is actually very good. In thinking about the larger prop turning less revolutions, you would avoid the cavitation problems also. If mounted in the center of a pontoon boat (Salvor 6 has a set up like this) I assume you would have the prop pointing downward, and skip the elbow part of the traditional mailbox. The elbow would be the greatest point of loss in the entire system in my opinion. Has anyone ever built one using a gear reduction? You could allow the diesel to run in its optimum power band, and gear it down to turn a much larger prop slowly. I assume some marine propulsion systems already use a gear reduction, but being inexperienced with larger boats, I'm not sure. At any rate, thanks for a compelling discussion.

Mac, I know what you mean about the JetSki's, I have a buddy who used to race them, and I would hold the ski at the starting line and release him when the flag dropped....I wound up on my butt more than a few times from the thrust those little things generated. Still they have a very focused (small diameter) column of water that they push, meaning they would blow a really small hole, making for some tedious hunting. In opposition to what Cornelius is talking about, you have a tiny prop turning very high RPM's. Do let us know what you get if you decide to tinker with one, but I think you may only prove Cornelius right...further adding to his ego Just kidding Cornelius.

Jason

 

[rgecy]

If mounted in the center of a pontoon boat (Salvor 6 has a set up like this) I assume you would have the prop pointing downward, and skip the elbow part of the traditional mailbox.

Jason,
I remember reading an article (I think in NatGeo) from back in the 60's or 70's that showed one of the contraptions Mel Fisher used on the 1715 fleet. It was a barge platform that had 3 large props mounted vertically under the platform. They would of course blow directly down to clear any sediment and reveal all the treasure.

I don't know if it was ever built, the article showed a sketch of the contraption and said that's what they used. But I have never seen an actual picture of it. Maybe someone could answer that for us and even find a picture for historical purposes.

Robert in SC

 

[ScubaDude]

Cornelius,
I'm not sure if you were alluding to this with part of your post ("setting the air valve") or not. With the ROV, couldn't use compressed air regulated to the interior of the ROV to eliminate depth obstacles like leaks, or crushing issues? Just keep the interior compartment a few psi above ambient and incorporate some form of safety valve for releasing the excess gas/air on ascent.

 

[Real de Tayopa Tropical Tramp]

=Cornelius ]
A mail box is not as simple as a lot of us think . Let me give you something to think about . 1) prop pitch 2) prop speed 3) prop diameter . Now start using your brains a little and come up with the right equation . Cornelius
*************

HI, most ship Chandleers / outboard engines / jet boat engine sales have nice easy charts/pamphlet's to handle that. Sub the weight /velocity of H20 to be involved for boat weight, water resistance ( hull design ) and speed formulae You can run the rpm's to the edge of cavitation for the type and size of the used prop.

Tropical Tramp

 

[Real de Tayopa Tropical Tramp]

Right on Cormelius. MERRY CHRISTMAS FELIZE NAVIDAD Y PROPERSO ANO NUEVO & A HAPPY NEW YEAR.

Tropical Tramp

 

[Salvor6]

Well here it is,

I finally have a picture of the center blower catamaran we built! it works great. The engine is a 18hp air cooled vertical shaft electrical start motor.

 

[stevemc]

The barge/blower contraption the the Real Eight Co used was in the early-mid 60s, That RGecy talked about, and it was the first blower for this type of work. Mel Fisher thought it up. It was intended to blow clearer surface water down and make work easier. But it also blew the sand away. The contraption had many draw backs, had to be towed, didnt work real good etc. It was a barge type boat, with a motor that had a vertical shaft, and a big unshrouded prop that turned slow enough to just push water to the depth that they needed. They then built what at first were called ashcans, and these were basicaly the same as mailboxes/blowers etc. I think because they used a metal garbage can to build it. (the ashcan name) I know when they did make that, it caught on and several people my dad dove with made their own, and they worked great. They refined the attachment and safety features to what they are today. On the Jetski thing, yes, they do have a lot of thrust in an instant, but you dont use a blower like that. You are just above an idle with diesels, (in shallow water)depending on the depth. You want to gently move off the overburden and leave anything else laying on the bottom. A jetski would need very careful throttle control to just move the sand and not have a tornado of sand. Kind of hard on the thumb. You probably would need a block or a screw stop to limit the rpm or adjust it in very tiny increments. It was used in 2-4 feet of water, and did not work real good, mainly because of the tight jet. They just used a 4" PVC elbow on the jet. They would spud it in place instead of anchors since they were in such shallow water. Speaking of blowers, I went by a high school near me yesterday and their HVAC system had several formed elbows of stainless or aluminum and it was maybe 12". Is it possible to get larger formed not welded elbows of aluminum? Could be a cheaper way to get blowers.

 

[ScubaDude]

The Rio Bravo has formed pipes for their blowers. Joe, any ideas where they came from, or where a brother might find some preformed elbows like that is various diameters?