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Old 11-27-2008, 04:06 AM   #21
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RE: Why semi-displacement (or semi-planing)?

FF, can you find a set at one of your flea markets? Where would you go to snag a used set?

They sometimes show up at flea markets , but the boards are better.

I purchased a small set ,with SS poles from RY on the PM board , but I have to move the dry exhaust to get them on C/L .

Found telescoping SS pipe , 10ft lower for 12ft upper and will mount them "in time".

There out there, keep looking.

AS noted above EGO and the add dept are the source of all these overpowered "trawlers".
Throw in a huge lack of understanding about the costs of this compromise and you get 35 -45 ft "trawlers" with 200-300+HP.

FF

-- Edited by FF at 05:09, 2008-11-27
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Old 11-27-2008, 01:01 PM   #22
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RE: Why semi-displacement (or semi-planing)?

Quote:
nomadwilly wrote:
How fast would your GB go Marin with 4hp per ton?
Well, in our case that would be about 52 horsepower.* I suspect that at our normal cruise rpm of about 1600, that's not much lower than what our FL120s are putting out.* Of course we have two of them so that makes something of a difference.* But I would suspect that a single engine GB36 being driven by 52 horsepower would reach or be just below hull speed.* Somewhere between 7 and 8 knots.* We cruise at about 7 knots on one engine at 1500 rpm unless the shaft is locked off (which we have to do if we're going to run more than about 10 minutes on one engine).
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Old 11-27-2008, 03:22 PM   #23
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RE: Why semi-displacement (or semi-planing)?

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Marin wrote:
nomadwilly wrote:
How fast would your GB go Marin with 4hp per ton?
* I suspect that at our normal cruise rpm of about 1600, that's not much lower than what our FL120s are putting out.(Marin)
Marin,
Aren't you eating turkey? What does that mean " I suspect .. putting out"? Are you saying your engines are making 52 hp at 1600 rpm? If so how do you know that? Do you have BW gears and do they suffer from free wheeling?

Eric Henning
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Old 11-27-2008, 03:44 PM   #24
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RE: Why semi-displacement (or semi-planing)?

Sloboat,

Very good copy from Krogen. The rest of you should read this and note that the semi-displacement in the example burns over ( at a higher speed though )*4 times as much fuel. I know most of you don't agree but I think the SD hull gererally burns about twice the fuel at the speed of a FD boat at typical cruise. Eric, I couldn't pull up the Shannon 38 site. Could be my favorite boat and I haven't seen anything about them for a long time. I'm very glad to see they are alive and hopefully well. Thanks for the post.

Eric Henning
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Old 11-27-2008, 04:07 PM   #25
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RE: Why semi-displacement (or semi-planing)?

Quote:
nomadwilly wrote:Are you saying your engines are making 52 hp at 1600 rpm? If so how do you know that?


*
That's what the power curves in the FL120 operating manual indicate.* It's actually more like about 60 or 65 hp.** More than your 4hp/ton but not that much more.
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Old 11-28-2008, 04:09 AM   #26
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RE: Why semi-displacement (or semi-planing)?

For old farm tractor engines like the Leman- Econo Power marinizations , operated at low speeds I would figure 16 hp /gal of fuel burned would be close., or a bit optomistic.

Most folks interested in economy never run hull speed as a slight reduction pays so well.

Reducing the speed from SL 1.34 down to SL 1.1 will usually pull fuel burn down 50% at little cost in speed.

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Old 11-28-2008, 06:26 AM   #27
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RE: Why semi-displacement (or semi-planing)?

Quote:
sloboat wrote:

Libertarian, have you considered adding stabilizers?*
I have, especially those fancy-schmancy gyroscopic ones.* But $50k is a hefty investment for a boat that might only need stabilization once in a blue moon.* I suppose if we were interested in regular long distance cruising in the ocean or great lakes, it might make more sense.* But we're at the dead end of the Potomac and even if we have the Roamer until we die, >95% of the time this will be a river boat and 95% of that time we'll be living aboard at the dock.
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Old 11-28-2008, 09:55 PM   #28
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RE: Why semi-displacement (or semi-planing)?

Sloboat,

I GOT THE*SRD 38 this time .. thanks. As to the disp/SD compairison I see the numbers .. had me scrachin my head for awhile but now I think I see the light. I think they wanted to slant the comp so they listed the fuel burn of the FD hull at it's hull speed. FD boats don't cruise at hull speed. Almost all cruise about one knot slower or very close to it. My own Willard*I cruise at 6.15 knots and 7 is hull speed. Nine knots is over hull speed for the Krogen 42 and cruising at " normal " cruise will burn far less fuel. Notice at the end of the next to last paragraph they claim the fuel burn for the K42 is 1.7*gph. The SD boat should shed about one gph from loosing a knot and that should produce more realistic numbers. That is .. a*SD boat should burn about 2 to 2.5 times as much fuel as a FD boat at the FD boats cruise speed.*Ops .. I see I compared a 48 SD to a 42 FD. That should change the numbers to about 1.8 to 2 times as much fuel. Still the FD boat should burn about half as much fuel at a speed/length ratio of about 1 to 1.1.

Eric Henning


-- Edited by nomadwilly at 22:56, 2008-11-28
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Old 11-29-2008, 04:43 AM   #29
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RE: Why semi-displacement (or semi-planing)?

"The Shannon design (http://www.shannonyachts.com/38faq.html is interesting in that he is making a serious engineering attempt to manage flow over the hull. Along those lines, I have to believe there are many other techniques to improve SD design efficiency that have not been fully developed because of cost. "

The Shannon is a simple but partial take off of the pioneering work by John Atkin.

His concept of reverse deadrise and a "box keel" pioneered the speed of SL 2.5 or so at the same fuel burn of a SL 1.1 snail boat.

Google RESCUE MINOR or Rob White , and in the small launch size , with light construction and a homebrew but efficient engine , over 30nmpg at 12-18K was reported.

Yes 1/2 gph at speed!

We have been working with a NA for a while now to incorperate the Atkin hull with light weight construction (under 8800lbs for the Euro reduced rules) and about 39 ft (just under 10 meters) with the deck beam of 7ft 6 inches and a bwl of about 5.5 ft.

This gives a Needle boat as Geere would call it , and if the computer can be believed incredable low fuel burn at speed.

Think 10K at 1 gph (yes about 20hp) and 18 at 3,5 gph!.

With the slender shape it will be a cruising boat that carries 8 , feeds 6, sleeps 4 (5 in a pinch) and cruises 2.

The scale model tests are yet to be run , to see how far off the computer is.

The box keel is great as the prop is totally protected (similar to the New Jersey Seabright style skiff) and take the ground naturally.
The box keel also equals loading/discharging* with simple pipe rollers , no equippment but a big push to load into a Sea Land box.


-- Edited by FF at 05:49, 2008-11-29
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Old 11-29-2008, 09:25 PM   #30
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RE: Why semi-displacement (or semi-planing)?

Slowboat,

As I said nobody runs at hull speed. At a knot below much much less*fuel is burned. FF IS a fan of SD. His Navy personel boat IS one.

FF
Is that boat of yours like a Hickman sea sled ?.

Eric Henning

-- Edited by nomadwilly at 22:28, 2008-11-29
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Old 11-30-2008, 04:51 AM   #31
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RE: Why semi-displacement (or semi-planing)?

How are you planning to get around Shannon's patent?

Shannons work is a poor copy of the Atkin boats of 50 years ago.


I simply purchased a copy of RIVER BELLE from Atkin's widow and computer squezed the hull to the dimensions I need. http://www.atkinboatplans.com/

For an idea of the performance claims for the hull design

http://www.robbwhite.com/rescue.minor.html

The underbody will be similar to RESCUE MINOR , but the hull from the WL up is quite different from River Belle as the service is different.

An idea of the hull in profile is STROLLER an early 1929 Herrishoff commuter.


FF

-- Edited by FF at 05:54, 2008-11-30
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Old 12-03-2008, 09:18 PM   #32
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RE: Why semi-displacement (or semi-planing)?

Marin,

Sorry to be so slow responding. Re: your message at the bottom of pg 3. Why do you think your power is actually 60 to 65 hp? Is the book wrong? The Ford or Lehman people don't even know where your engines are. How could they predict how much power you'd be taping off. I think we've been here before. The hp curves for your engine are made on a dymometer .. every one of the dots connected to make the curve are measurements made at WOT. Fuel consumption may or may not indicate how much power your'e delivering to the flywheel. If your engines make 52 hp at 1600 rpm at WOT we can only make guesses as to what power is being delivered. One thing is for shure .. it's much less .. probably about 30 hp.*I wonder what the GB 36 weighs .. 12 tons ?*Maybe 14. A*Willard 40 takes 23 hp to make 7 knots and it looks like the GB 36 takes about 60. The Willard weighs over 16 tons and is bigger over all. Looks like a FD hull takes only about 1/3 that of a SD hull.

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Old 12-04-2008, 04:56 AM   #33
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RE: Why semi-displacement (or semi-planing)?

The easiest way to gueestimate HP is by measured fuel consumption.
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Old 12-04-2008, 09:58 PM   #34
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RE: Why semi-displacement (or semi-planing)?

FF,

What a treasure .. the Atkin site. Iv'e spent some time there. I browsed his books a lot when I was about 12 in a library in Seattle. Thanks for the link.
Why are you so*sour on the Shannon SRD? The only room for improvement is a fuller bow with more flare. I see a slight resemblence to Windhorse and as*I recall you don't like that one either ... what gives.

Eric Henning*
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Old 12-05-2008, 04:26 AM   #35
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RE: Why semi-displacement (or semi-planing)?

Wrong guy,

I think WINDHORSE is a great example of what the 1 -1000 (1-1,000,000?) true offshore cruiser should be.

The cabin folks would have a heart attack about paying for a waterfront spot not 3 or 4 stories tall. Not ME!

The web site for the WH folks is a fine source of info .

"Why are you so sour on the Shannon SRD?"

AS a recovering New Yorker I can spot BS , ad hype and copy artists a mile away.

That's what us City folk learn in the 3rd grade!

While the "Carolina Sport Fish" bow flair might be excessive , we found the style of many of the "Lake Union" boats the one to steal for the boxboat.

Another steal , first saw it on the MIDNIGHT LACE , and later on the H drawings for STROLLER is a bow cockpit.

On boxboat there would only be enough room for a "rumbleseat" style , to fit 2 , but it will work as a bow well for anchor handling (good on a narrow foredeck) .

With a good design it could help as source of air for the fwd cabin , even in heavy rain.

With a baby buggy cover and small wind screen it would make heavy weather more interesting than slouching in the PH.

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Old 12-06-2008, 10:47 AM   #36
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RE: Why semi-displacement (or semi-planing)?

FF

Maybe you should go back to the 3rd grade and get your BS sensors adjusted.I think the planing Shannon is a fine design if not brilliant design but thats just an opnion too.
As for the forward cockpit I let a gal whose exuberance for boating went amuck as she wanted to stick up through the fwd hatch on my previous boat in semi rough going. I said yes as she was like a little kid tuging at my sleves all excited .. she paddled kayaks and really loved everything " boat ". As expected the big one came along and soaked her but not the smile .. actually she went to laughing. I'll be following your design and thanks again for the Atkin site.

Eric Henning
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Old 12-07-2008, 09:49 AM   #37
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RE: Why semi-displacement (or semi-planing)?

Eric:

I have spent considerable time reviewing the Shannon design and although, for the most part I like it, my own experience says "no port lights or engine air intakes on the outside of the hull." (I noticed that your boat qualifies in this respect.) On my previous Ocean Alex (which my wife still loves) we always had someone, even us, forgetting to close a port lite when the boat was underway. (At 20 knots this can make for one wet stateroom). In windy beam seas, the experience was the same as well as taking water in the engine air intakes. I know there are a lot of boats that have "holes" in the hull for venting and most of the large multi million $ yachts do this all the time but my experience on the smaller vessels says "keep all the venting and engine air intakes inboard.

My opinion

Walt
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Old 12-07-2008, 05:07 PM   #38
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RE: Why semi-displacement (or semi-planing)?

Hi Walt,

I took another look at the Shannon and have a different take on it now. I think the hull is as wonderful as ever but Shannon being a sail boat manufacturer .. *thier minds are stuck in the rag boat box. After thinking about it I wouldn't even want a Shannon. Like a sail boat if your'e not on the bridge or in the aft cockpit your'e down in a hole barely able to see out. Not for me! The stern looks more like a hot tub than a boat and visibility is probably a bit shy under way. I'd go for a 23' version with a Sea Dory style cabin. About the ports and vents I think thats like bootin Goldie Hawn out of bed with a wart on her toe. Bet you wonder how I know that huh.

Eric Henning
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Old 12-08-2008, 03:59 AM   #39
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RE: Why semi-displacement (or semi-planing)?

Most marine motorists prefer big high boats 3 or 4 stories tall, with an oxygen tent and big dink on top too.

Fine dockside , fine on a lake or bay , or some other VERY protected waters.

But even lake Michigan or the GOM will pop up 8-10 ft waves with a 7 -8 second period.

Much ungood in one of those condo boats.

The ride will still suck in a more rational boat , but at least the danger factor and FEAR factor would be lots lower.

In a well designed and built cruiser the ride might not be that bad, AP steering and stabelizers working up a storm.

FF
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Old 12-08-2008, 07:46 AM   #40
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RE: Why semi-displacement (or semi-planing)?

Eric:

Pick someone else......I'd boot Goldie Hawn out of bed for a much lesser offense than you've named.
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