North Pacific Trawler 39 getting rolling chocks

[DDW]

Boat builders don't like multipiece molds. You have a parting line to finish, and that's not a good think in a female mold gelcoat boat. For series production you could just mold a separate piece that fits, and bond it on with Plexus.

People keep worrying about two things: slings and hitting the dock with them. At least with the Independent Shipwrights version, ain't a problem. Don't worry about it.

On his, they drill holes in them to let the flood so they don't change buoyancy. I plugged the holes with set screws as I think I want the buoyancy. Can always remove the screws and let them flood. I calculated mine at about 300 lbs net buoyancy, (400 lbs volume minus perhaps about 100 lbs of laminate).

 

[JDCAVE]

The work continues. I think the owner is a bit frustrated by the speed of things, but the FRP guy is working on commercial fishing vessels that are on schedule to go north.



Jim

 

[Northern Spy]

Great discussion. Regarding hull molding, I don’t see why it would make a huge difference in mold releasing, it may require a multi piece mold but that’s not hard. Regarding dock bashing, I don’t see why they need to be so far out from the chine?
They seem like an exceedingly good idea to me, and as we have a no-keel aluminum boat, I’m definitely thinking about fitting some on my bottom. I’d have an issue of strength however, and bracing them with struts presents issues, so I’ll have to think about that. I may need to make them in two pieces and bend them together at the tips, sort of like canoes welded on bottom.
The picture of the boat beached resting on its two wings is very appealing to me. I love the idea of a tide safe boat where you can beach it, work on it while tide out and then wait for water to come back. So cool.

They are far out on the chine likely for two reasons.

If you are trying to dampen roll acceleration, it would make sense to do it on the outermost radius, where the velocity is the highest.

Secondly, the way they work is creating drag by creating an eddy on the back side of the chock. If the chock is not in free water, eddy formation (or size) would likely be dampened by the adjacent hull and decrease the effectiveness.

Bilge keels are common in tidal European harbours for the reason you mention. But generally the basins have soft bottoms when they dry.

 

[DDW]

That does seem to be taking awhile. The ones I just had done by Independent went on in a day - started at about 0730 and done by 1700. They did not put the finest finish on them to be sure, proper fairing would have taken another day. But as they said, it makes no difference except for boat yard points.

 

[DDW]

I'll probably start a new thread in due time, but I launched my boat today, first time in the water with the rolling chocks. Not a rough crossing, but my preliminary feeling is that the chocks make a very noticeable difference. When crossing ferry wakes rather than several cycles of quick rolling, it would roll to one side, then just settle back to level. All of the rolling seems slower and considerably dampened, like it is a bigger boat. I really need some nice rolly conditions to test them out.

There seems to be no difference in speed, consumption, or low speed maneuvering (I tested all of those). There is a little more thumping over a light chop, it would do that before in the right conditions but seems to do it in wider conditions now. At max throttle the spray pattern is different, some coming off the leading edge of the chock and a small rooster tail from the trialing edge which wets the dinghy stem and stern. I don't recall that before. At max cruise this has gone away and it seems pretty much the same. I'd thought the trim on plane (SD plane) might be different but it is not. As I thought, there is no issue with them hitting a dock, you'd contact the topsides first or at the same time, fenders hold them off as well as the topsides.

 

[long-cours.62]

Thanks for your "retex" as I wrote before , we fil the same after added our's. But we do few things at the same time and don't know how much for each added things
But we fill exactly the : one roll end stop , no more few roll , dampened quicker.