BILGE BLOWER THRUSTERS

[Carlos D]

Gents, I'm almost finished with my ROV, the thrusters are ex 500gph bilge pumps
mated to 50mm model boat props which seem to work well. I also tested a bilge
blower in the water and it produced strong thrust. When you look at it, what
you have is a multi blade kaplan prop in a houseing which resembles a Kort Nozzle.
I've used the motor several times with no problem. You do have to rinse it with
fresh water, and add WD40 after each run but there are no seals or leaks to deal
with. West Marine has them, they are a little steep in price but remember it is a
complete unit with nothing else to buy, and the motor itself can be replaced for
7 bucks! The housing also has a flat section that is perfect for mounting o an
ROV! Check it out!

[Pilikia]

Hi Carlos ~ I bought one of those in-line bilge blowers (3" Rule model 140) on the off-chance it might make a good thruster. I haven't had a chance to test it yet. I'm encouraged by your report. I like that the blades are in a housing and that it has built-in mounting brackets, as you mention. At $7 for a replacement motor, it seems likely to be an economical solution in the long run.

Would you say the thrust is comparable to the bilge pumps with model props? Any idea how much power it draws when it's pushing water? Where do you put the WD-40? How do you remove the motor? It looks to me that where the wires exit the motor housing could be sealed up, maybe with silicone. Please keep us posted on your experience with them. --Pilikia

[Carlos D]

Hi Pilikia, I haven't tested the bilge thruster's amp draw yet but I imagine it will be
higher than my present setup. I use a 125 amp hr deep cycle batt with my unit so
I'm not that concerned about amp draw. When I tested it, attached to a 2x4, and placed it in the water I was surprised by the amt of thrust it produced, I had to hold it with two
hands! The design closely resembles a Kort Nozzle with it's multi blade kaplan prop in the nozzle. I know that the prop shroud is not hydrodynamically airfoil shaped as is the case
with all Kort Nozzles, but it will kick out thrust like a champ!
OK, to disassemble the unit, you need to wedge a flat head under the prop hub and SLOWLY pry it off. Next you'll see two screws that hold the motor to it's housing, back
them out, then pull the motor out from behind. I have used the motor for 12, 15 min
cycles over three days with no problems. At the end of the day I dissasemble the unit,
rinse the motor in fresh, clean water, run the motor to drain out the water, then add
WD40 to one of two ports at the end. Next I run the motor for a few minutes to
heat it up and circulate the oil. That's it!..... I know the motors will eventually fail
but the 7 buck replacement won't kill me and with no seal failures to worry about they
will dive DEEP ;-]

[Pilikia]

Here is a photo of the promising bilge blower we are talking about:

[bigbellydude]

Hi All,

I am participating in the MATE ROV contest in California, and my team is looking for bilge pump motors to use. We are looking for 3 minimum, but we have money constraints. Are there any "good" pumps out there to be had for under $15 apiece?

[Pilikia]

Check out eBay Item No. 320619209090. Description leaves unclear if they have more than one, but says it is inventory reduction from bulk purchase, so maybe they have a bunch.

[sthone]

I like the Mayfair line of replacement cartridges available from Cabela's. I think they are a little easier to use over the Rule pumps as they don't need to be cut up to be used with props. You just need to find a prop and adapter and your good to go. I usually go with the 750GPH models (which are about $20) but they do have a 500GPH model which is in your price range.

http://www.cabelas.com/product/Johnson- ... tt=mayfair

-Steve

[bigbellydude]

Hi All,

Thanks Steve, for the link. I looked it up, and it is definitely in our price range. The Amp draw is perfect, since we have a limit of maybe 25 amps. Voltage is good too... However, just for the sake of asking, how well would this do under competition conditions? Does it have a good "rate of acceleration", or whatever you would call it?

Also, where could we find a good prop and ????what is an adapter???? Sorry for my ignorance

[sthone]

I think they will work fine for use in competition, actually lot of the Ranger teams use them all ready.

I've tested a lot of different props on these pumps, you can see my results on this page...

http://www.homebuiltrovs.com/mayfair750test.html

The props I like the best are a plastic 50mm 3 blade boat propeller made by Robbe which I found at http://www.harbormodels.com/

No matter what kind of prop you select you will need an adapter to attach the prop to the motor shaft. Most bilges pumps (at least the few I have used) have an solid 1/8" motor shaft, and then the type of adapter you use will depend on the props you choose, they may either be threaded or just have a hole through them.

For the props that just have a hole through them you can usually find a store bought adapter from hobby shops or places online like Tower Hobbies and they will look something like this.

astg1700.jpg (14.19 KiB) Viewed 9052 times

The adapter would just slide over the motor shaft and be held on with a set screw, the prop then slides onto the adapter and is just held on with the nut.

For props that thread on (such as the ones from Harbor models that I use) you will probably need to make your own adapter such as this

bilgeconversion8.jpg (26.73 KiB) Viewed 9052 times

Making your own adapters usually requires the use of a lathe to machine though. If you do have access to tooling these are the specs I use to make mine.

bilgeadapter.jpg (45.16 KiB) Viewed 9052 times

There are ways to make threaded adapters without a lathe but I'll save that for another thread so if you go that route just let me know.

-Steve

[bigbellydude]

OK, thanks Steve. I just looked at this thread title, and it says Bilge Blower Thrusters, which we did look at, but doesn't quite fit in with this topic. I'll continue on a different Thrusters thread. Thanks