Build vs. buy a mailbox for moving sand?

[daylorb]

I completed my dredge project and it is working well - 3" suction dredge designed to clear out sand from boat dock area.

Now I'm on to bigger things.... I'm looking at blasting a channel roughly 100' long through some shallow spots and think a mailbox design like this one is going to be much quicker... http://www.treasurenet.com/forums/shipwrecks/378545-cheap-down-dirty-mailbox.html

Question - does anyone build these/sell them?

My plan is to build one similar to this, potentially case it in fiberglass wrap to beef it up (will get repeated use), but before I go to all of that trouble, wonder if there is another option?

Thank you!

 

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[Lycof]

My first thought was that you better not expect that motor to last long.

Blowing that much sand into the water column will most likely get a lot of it sucked into the engine cooling system and destroy it.

 

[daylorb]

My first thought was that you better not expect that motor to last long.

Blowing that much sand into the water column will most likely get a lot of it sucked into the engine cooling system and destroy it.

The plan would is going to be to put ear muffs on the outboard, run a hose to the bow, attach a submersible bilge pump and run water through it that way in an effort to keep the intake away from the sand. Probably put it in a cheesecloth bag.

 

[Jason in Enid]

One thing to keep in mind is the thickness of the metal you are going to use. I've seen people try to use cheap, thin sheet-metal with terrible results. Remember that for all the power going out the end of the mailbox, there is an equal vacuum at the front.

 

[daylorb]

One thing to keep in mind is the thickness of the metal you are going to use. I've seen people try to use cheap, thin sheet-metal with terrible results. Remember that for all the power going out the end of the mailbox, there is an equal vacuum at the front.

That is a chief concern. My neighbor (who will also use it) has a machine shop and is going to fabricate it. He's got a bunch of 12" diameter heavy steel pipe scrap from another project. Plenty to do this one. It is plenty durable, really, really heavy.

Trying to figure out if that is big enough - my prop is 12". My gut tells me I should have larger tube diameter than 12" but it is pricey.

Any thought on size required?

The other option is to build it out of 14" duct elbow, have him either weld a frame around it, or glass it up with chopped strand and poly resin - effectively use the duct for the frame and reinforce with the fiberglass.

Thoughts?

 

[Jason in Enid]

No thoughts on trying to reinforce thin wall with glass, never thought about that before. A 12" pipe over a 12" prop sounds troublesome. That doesnt leave any "wiggle room" for shifts in exact duct placement.

As for efficiency, theoretically, the 12" pipe over the 12" prop will work but you are giving up a lot of "free work". If you have an oversized mailbox, then the prop wash blasts down the middle and carries more water down with it. We use the same principle in firefighting when drafting. Its also the same idea in gold dredging of putting a small high pressure discharge into a pipe to create the suction on the nozzle. I'm sure there are calculations to give you the optimum size but I have never seen them.