Sea Sled madness. It’s in my brain.

Discussion in 'Fiberglass and Composite Boat Building' started by DogCavalry, Nov 11, 2019.

  1. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    IMG_20220928_133849381_HDR.jpg IMG_20220928_083203974_HDR.jpg IMG_20220921_100229270.jpg IMG_20220928_133903284_HDR.jpg The job.
     
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  2. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    IMG-20221001-WA0003.jpg
    More Indian Arm stuff. Taken from Serenity, so technically Sea Sled related.
     
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  3. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    @baeckmo , any thoughts on a pod or fin to clear the bubble field and provide the lower leg with green water? I'm having a hard time visualizing a flow that simultaneously clears aerated water while pulling in green water. However I know that this solution was successfully implemented in many boats, so it's simply a failure of visualization on my part.
     
  4. fallguy
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    fallguy Senior Member

    Unfair.
     
  5. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    I think it's best if you come and judge for yourself. I'll put some extra craft beer in the beer fridge.
     
  6. baeckmo
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    baeckmo Hydrodynamics

    Yes, but have to come back later about it.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    It would be unwise to add any words to describe this truly stunning scene...
     
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  8. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Everyone reading this is invited. Nothing would make me happier than to have my forum comrades riding up Indian Arm in Serenity with us, eating salmon or crabs or prawns we caught ourselves, sleeping in the guest rooms, warming up from a swim from our dock in our hot tub.
     
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  9. baeckmo
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    baeckmo Hydrodynamics

    About the pod: I've used a "collar" to deflect saltwater ice from waterjet inlets, and I see similarities between this and the aeration problem. The first two pic's show the pod/collar with the opening to fit the jet inlet. Next I have extended the "roof" to the AV plate level for the Serenity OB application.

    Drawbacks with the pod are that you can not "park" the hull on the dry, like a container anymore, and there is of course an increase in resistance. The alternative, the lengthening of the OB leg, is interesting since it may be an easier approach. ....... and the pod has to be fastened to the hull just in the region where someone has placed a fuel tank, which complicates things....
     

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  10. fallguy
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    fallguy Senior Member

    Wow. That is not what I expected.. Is much larger and more invasive. Not meaning to offend...just not what I pictured..

    Can I ask a dumb question? @baeckmo

    What about something like an 8' angle iron made with 316ss, bent to conform to Serenity's needs, like a longitudinal interceptor. Would that not be enough to force the aerated flow away from the middle? It would be placed on each of the hulls inside where the aerated flow comes off the hull.

    Yes, some resistance, but seems simpler. It would be more like a strake.

    Or does that create more problems?

    The deeper leg would work, most likely, but would cause some extra drag as well. So the ideal is a deeper leg that can be lifted up on a jackplate
     
  11. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Thanks @baeckmo . It's longer than I visualized, but essentially the same. Unfortunately some short sighted builder installed a fuel tank through that area. Well, epoxy is pretty sticky.

    @fallguy I think a structure like that would just make turbulence and drag. The water would cross it, rather than going around, with the turbulence carrying the air deeper, and breaking up whatever stratification is currently happening.
     
  12. baeckmo
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    baeckmo Hydrodynamics

    It's possible that it can be tweaked a bit to reduce the size and make the shape easier to crate. Will continue scratching.....
     
  13. fallguy
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    fallguy Senior Member

    okay...I wonder one small other question...

    if you had skegs on the hulls; would that be much different than the pod? The pod, as drawn by @baeckmo , is all the way around the boat, so this must imply the flow and bubbles begin further away, so what about just a deep skeg say 3-4" or some less speculative guess?
     
  14. baeckmo
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    baeckmo Hydrodynamics

    The pod, as drawn, is about 400 mm wide, plus 2x50 mm flange, and its length roughly 1200 mm. I don't feel that is "all the way around the boat". The original setup stands 60 mm clear from the bottom, and caused a top speed reduction from 21 knots to just below 20. We also found it to be effective in deflecting floating debris, which normally causes frustrating loss of powering at the most inconvenient moments.
     

  15. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    The hull is 10' wide, 8' from chine to chine. The middle ⅓ of the area behind the transom is foaming. Port and starboard of that it's green water. The foam comes from air ingested at the front end of the tunnel. Skegs on the chines wouldn't do anything. Ironically for most sea sleds all this air is a huge benefit. But most sleds, at least historically, don't try to run their engine in this foam. And in normal years, when mid sized outboards are commonly available, I wouldn't have either.

    The extra leg extension will certainly cause some drag too. More or less than the pod, I can't say. I will say this though: dragging my sea snake on a broom handle at only 7-8 knots made enough drag that it was hard work. I shudder to think how much drag that massive leg makes. Fortunately it's dragging through low density foam, but still. It really brings home how much Hickman's SPP arrangement must have improved the performance of boats a hundred and ten years ago.
     
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