HMD 21 starting - help

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fallguy1000
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Re: HMD 21 starting - help

Post by fallguy1000 »

Waste water tank is best double vented. One vent each side of boat. Mine will be...

Your drawing is the wrong angles. Put two stringers under the tank and a small flat section.
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duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

fallguy1000 wrote: Mon Jun 21, 2021 3:20 pm Waste water tank is best double vented. One vent each side of boat. Mine will be...

Your drawing is the wrong angles. Put two stringers under the tank and a small flat section.
U mean like a bridge i guess. I think i got it. Thank you 🙏

fallguy1000
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Re: HMD 21 starting - help

Post by fallguy1000 »

duysall83 wrote: Mon Jun 21, 2021 4:27 pm
fallguy1000 wrote: Mon Jun 21, 2021 3:20 pm Waste water tank is best double vented. One vent each side of boat. Mine will be...

Your drawing is the wrong angles. Put two stringers under the tank and a small flat section.
U mean like a bridge i guess. I think i got it. Thank you 🙏
All waste stinks. But anaerobic bacteria exist when no oxygen is present. And they stink much worse.

Dual venting blackwater is the ideal. Another improvement is clam shelling the vent intakes open on one side and closed on the other to force the cross vent. I might just use thru hulls, but I also may put a clam shell over one of them to force odors away from the center of the ride.
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TomW1
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Re: HMD 21 starting - help

Post by TomW1 »

Fallguy totally disagree with you on needing two vents. You only need one vent so that the tank does not develop a vacuum. That vent should be led on an upward angle to the rear stern quarter with a clam shell over it so that water can not make egress into it. You do not need cross air flow in the tank. Think of how a septic tank works. It outlets to the the drain field.

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fallguy1000
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Re: HMD 21 starting - help

Post by fallguy1000 »

TomW1 wrote: Tue Jun 22, 2021 12:29 am Fallguy totally disagree with you on needing two vents. You only need one vent so that the tank does not develop a vacuum. That vent should be led on an upward angle to the rear stern quarter with a clam shell over it so that water can not make egress into it. You do not need cross air flow in the tank. Think of how a septic tank works. It outlets to the the drain field.

Tom
Peggy Hall is the 'potty princess' and she says multiple vents and no higher than a 3' rise to the vent is the secret.

Why?

In a houseboat or camper, when they run the vents to the ceiling; it creates an air lock. The gases get stuck and then only anaerobic bacteria work and they wreak like s..t.

A septic tank for a home stinks like hell; there is no comparison.

People get confused. Blackwater tanks stink because the bacteria that live in a non-oxygen tank are really stinky, but aerobic bacteria in a well oxygenated tank work fast and you add an odor killer to the tank and they work faster.

If the OP does it right, he can vent the tank from each side. Water ingress doesn't matter, generally. While it is certainly not desired, a little water entering a tank doesn't change much and is far better than running the vent to the roof.

Another reason to put the blackwater tank firther aft onboard is the odors will be leaving while underway. The ideal is as far back as possible. Combine that with dual vents and enzymes and proper vent placement and tanks are not terrible.

Don't disagree if you haven't done the research my friend.
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Re: HMD 21 starting - help

Post by Jaysen »

Alternative solution… composting head. That’s my solution to the whole problem.
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fallguy1000
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Re: HMD 21 starting - help

Post by fallguy1000 »

Jaysen wrote: Tue Jun 22, 2021 9:38 am Alternative solution… composting head. That’s my solution to the whole problem.
Yes. The problem for me is I would be the only one cleaning the coffee filter misses/overages. No thanks.
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duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

Hello all,, little progress. fuel (fwd one) and water tank seat and compartments almost done. Also i have a question. Can i fill the area under the berth (triangle one toward bow) with concrete. by filling i mean at least till surface levels. Also may serve as ballast? Motor will be 50-70 cm further aft compare to the original place. So that i guessed putting some weight in advance may be logical.

Thanks,
Duysal
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cape man
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Re: HMD 21 starting - help

Post by cape man »

I would prefer removable ballast, and add it as needed after you launch and see how she sits and rides.
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Re: HMD 21 starting - help

Post by Doug N »

Hello Duysall. I made another small compartment forward of frame e that is about 12" front to back but full width of the hull. I put 3 ten litre plastic gas cans full of water in there, through a small hatch, for ballast. Close to 70 pounds of water as they are filled to the brim. That really levels the boat out. If I was creative and used a bladder of some sort, I think I could get in about 150 pounds if needed. This way it is quite adjustable.
I left the small area that was left forward of these compartments for flotation foam. Sorry I don't have any pictures before the berth top went on.
DSC_3738.JPG
The small hatch is the one I'm talking about. The small deckplate forward is to get at the back of the bow-eye nuts/washers.

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