Twin-screw Goliath Idea

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aero_dan
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Twin-screw Goliath Idea

Postby aero_dan » Thu Apr 25, 2013 3:14 pm

It was suggested I re-post my question here from another section (Hankinsin designs), due to its relativity here, being a steel build... But it is a power, and keel mod question too. So I wonder if I should post it in the powered section too?

Here it goes:
I will be starting building a Goliath this year, in steel, if all goes well. I wondered if it might be possible to make the drive-train a twin-screw (or jet), with a good width between shaves, (let's say 3' for discussion), to allow for a through-hull hoist-way to lift & lower heavy work through the boat, w/ bottom doors. I thought this would be great to lay dock anchor drums, or salvaging of lighter oversizes objects like sunken boat parts, engines, etc on the lake. Would it be possible or practical to make this mod? I would think having twin screws or jets would make it ultra maneuverable too. I have made some preliminary sketches including a mast & boom or fixed gantry, but being an uncertificated engineering type, I know better than to trust some of my ideas. Anybody care to speculate with me here??
Better, faster, cheaper. Only ever found 2 of the 3! (But still lookin.)
So many boats, ...so little time.

Trackhappy
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Re: Twin-screw Goliath Idea

Postby Trackhappy » Thu Apr 25, 2013 4:07 pm

The only thing that I can think that may be a hidden issue is the change in the centre of buoyancy and overall displacement as you will be removing some underwater hull area down aft. I am not familiar with the design obviously, but if you remove part of the keel then you need to re-establish the basic strength of the hull by compensating around the area you cut out, which is something not to be taken lightly, and also allow extra strength for the torque of the engines transmitted through the structure. Two engines will also add more weight aft, where you have already lost some buoyancy. 3 feet in between, then an engine either side, will you have enough width down low to fit it all in?

Please note that I am not an expert, just thinking things through.
By the time I have built a boat, I'll be ready to build a boat....

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aero_dan
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Re: Twin-screw Goliath Idea

Postby aero_dan » Thu Apr 25, 2013 4:53 pm

I had considered these issues, thanks. I had thought, since the ballast/keel was an add-on after the hull was formed, to relocate two similar ones along the new centerlines of the engines. given that a small marine powerplant like what is found in a typical late-model jetski is usually under about 24", I thought there might be enough remaining room. If I understand right, 2 of these units weighs about the same or less than a typical marine diesel system like a Westerbeke or Universal. 2'-9" X 3' X 3'= 185.625# of lost flotation, I think. Am I forgetting so far?
Better, faster, cheaper. Only ever found 2 of the 3! (But still lookin.)
So many boats, ...so little time.

slug
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Re: Twin-screw Goliath Idea

Postby slug » Sun Apr 28, 2013 4:33 am

Rather than fool with an untested approach that to me has a lot of potential problems associated with it, why not just build in a substantial crane/hoist/davit to raise or lower objects over the side ( or stern )? Much simpler and won't make the finished product a "one-off" oddball for resale later.
Trust me, building this boat as is , is enough of a challenge.
Here's a Titan in aluminum that I looked at before I decided on mine. Note the boom used for hauling.
http://www.gtbay.org/our-programs/grand ... baykeeper/

Doug

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aero_dan
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Re: Twin-screw Goliath Idea

Postby aero_dan » Sun Apr 28, 2013 9:40 am

Thanks Doug, I sense an air of experience in your thoughtful response. I appresiate the input. I had drawn a dry stack and boom-mast on my proposal too.
Dan
Better, faster, cheaper. Only ever found 2 of the 3! (But still lookin.)
So many boats, ...so little time.


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