Jersey Sea Skiff Performance?

[FAST FRED]

I have been reading the Pocket Cruisers thread , and trolling the web and believe that the Jersey Sea Skiff hull under body has lots to admire.

The DISTURBER ,by Atkin & Co, described in Jan 1960 Motor Boating , would skim over sand with no damage to the running gear , and was claimed to be a fine sea boat in rough waters.


The Tolman Skiffs , seem to be a variation , but designed for outboard power.

I wonder what this very useful hull shape " costs" in terms of running efficiency?

The designer claimed it was far better (25%+) than a conventional hull and some Austrians with a similar "Power Glider" claimed low wake , good speed and modest fuel consumption.

I'm almost finished with a scaled down interior for STROLLER ,to have her fit into a container (39 x 7.6 and under 9ft high fits).

The cruising advantage of a large flat section so she can either take the ground overnight , or at least be easy to roll into a Sea Land box for transport is very desirable.

With a "trailer" weight of 8000 to 10,000 lbs (no fuel or water) the DL should be low enough , and the BWL fine enough for cruising at SL 2.5 or 3.

So the question is what fuel consumption penalty , over a "conventional" hull would this Jersey Sea Skiff bottom cost?

The quest is for a boat that can cruise at better than 5nmpg at SL 3.

Am I dreaming?

FRED

[FAST FRED]

This is the article from Motor Boating that sparks the interest.

FF

[tom28571]

Well Fred, Looks like no one is too interested in the Jersey Skiff just yet. This topic has been discussed several times on this and other forums. I think this hull form has a lot going for it. It's the same basic form as "Rescue Minor" that Robb White built. It should make a very efficient mid-speed cruiser that works well in shallow and deep water. I doubt that it is good for speeds much over 20mph but under that, it should work well. I've heard that the Jersey shore fishermen used the deep flat center section to allow launching off the beach over rollers, protect the propeller and keep weight low at the same time. Sounds like a good deal to me.

[kerosene]

Hey I find this very inetrresting - however with my limited knowledge I cannot provide any relevent input...

I wonder how big you can go with this kind of hull. When I grow up and move to some place where one can buy more than one bedroom for 500k$ I want to build some sort of weekender - efficiency for me is a key issue.

h

[Willallison]

Fred, Have you looked into any of Dave Gerr's boats? He has a number that are variations on the Jersey Sea Bright Skiff. I think he discusses them a bit in The Nature of Boats

[FAST FRED]

I have The Nature of Boats in my library , and was impressed with his design. But I don't think his will run over sandbars with the ease of the Atkin..

20K would be a great speed , if it could be done on about 100hp , a modern engine would need about 4gph , giving a nice affordable 5 nmpg.

Slowing to 14 or 16K should do even better, and of course "LRC get home" at 7K would barely move the fuel gage!

FF

[SAQuestor]

Fred,

Actually I think this whole concept could fit right in with the Pocket Cruiser thread and the now nearly extinct Option One thread.

As a friend of mine has told me repeatedly, “What’s under the water is important – What’s above is just aesthetics.”

Given that repeated admonition, let’s speculate a bit and see if this sparks a conversation.

I want a boat that is transportable from coast to coast. Not necessarily trailerable to the local pond for an afternoon’s joy ride.

That boat must be comfortable enough for extended trips – durations of 8 to 12 weeks. But like so many other folks that have a bit of gray in their hair (or lack very much on top:eek: ) comfort is a personal thing in that some folks might still like to tent camp and some folks want a four-star hotel. Me? I’d be happy with a dry warm cabin, a nice strong cup-o’-joe and a comfortable seat to watch the rain fall in June while back in some fjord in BC or Alaska. And enough vittles to be able to stay away from a town for a couple of weeks.

But the boat should also be sea worthy enough that a bit of wave and wind blowing down one of the straits up north would not necessitate scurrying for an anchorage. (Not that I am advocating being stupid and ignoring worsening conditions.)

Range? 300 to 400 miles at a reasonable speed?

Speed? What’s reasonable? For some folks it’s 20+ knots. Others might be content at 7 knots. For me, reasonable falls into the 10-14 knot range.

Economy? Were “I rich beyond the dreams of avarice” -- Edward Moore –- then I wouldn’t worry too much about building and fuel costs. But being an average computerized desk-jockey I do have to watch both the build cost and operational costs. I’ll address build cost below – but my spreadsheet suggests that if I can average about 5 MPG then the fuel costs will be in the range of .66¢ to .75¢ per mile. Of course fuel cost per gallon, speed and sea conditions will play a major role in the variability of this, but I did calculate very conservatively.

Tom and I have corresponded some good bit about his Bluejacket designs. As you might know, Tom has a new 28’er is out in plan form and if I’m willing to take a bit less of the ‘comforts’ along, we both think that it’s just about a perfect boat for cruising a part of the Great Loop a couple of summers from now. Then heading to Alaska the following summer and then exploring south Florida in the winter – yada, yada and more yada.

As we all know, Tom has written extensively about his BJ24 and the reasons for that design, its goals and actual accomplishments. Look in the Option 1 thread and/or do a search for tom28571.

Tom has designed a full planing hull form that performs in a very remarkable manner. Full planing at low speed is a key characteristic. Because the BJ24 planes at a nearly flat angle of incidence, the wake – whether at 12mph or 22 mph is –compared to a deeper vee fiberglass production design – nearly non-existent. Please see the videos that Tom has so graciously given permission to put on youtube.


Liz accelerating from slow to full speed - about 22 MPH (http://www.youtube.com/watch?v=6OzDpbMJM0c).

Liz accelerating from stop to full speed - about 22 MPH. (http://www.youtube.com/watch?v=6Hd8sbIGRbQ)

Liz ‘cruzin’ - about 12 MPH. (http://www.youtube.com/watch?v=XkILP1nxEdg)

Liz passing by at full speed - about 22 MPH. (http://www.youtube.com/watch?v=Fb0I_Bjg5JE)

Liz passing by at full speed #2 - about 22 MPH. (http://www.youtube.com/watch?v=lfn7QyufFQU)


There are several features on Tom’s design that all add up to an efficient – in terms of fuel usage per mile – boat. The shallow vee and chine flats have been discussed ad-infinitum elsewhere.

As I believe most, if not all of us that are interested in boat design will agree, bottom loading is a vital key to securing economy and performance from a semi-displacement or full planing hull form.

This is where I’m still struggling a bit – the amount of ‘stuff’ that I feel like I need to tote along when going away from civilization for a few weeks will degrade boat performance by increasing the bottom loading factor. Tom’s boats are designed with a BLF of about 18 lbs/sq.ft. at rest and increasing to the mid to high 20 lbs/sq.ft. on plane.

Other folks that are quite knowledgeable concerning boat design stuff, and that I have faith in for not leading me astray, also suggest that this range of BLF numbers are in line with some of the more efficient semi-planing/semi-displacement hull forms that have been admired from afar, witness Whio. (http://www.amateurboatbuilding.com/articles/design/whio/whio.html)

Take a stroll over to Tom’s website (http://www.bluejacketboats.com/) where he has a new treatise on planing hulls (http://www.bluejacketboats.com/planing_boat_theory.htm) posted.

Fred, if you’re not too set on taking lots of ‘stuff’ along, you might seriously consider Tom’s 28’er as a suitable candidate. Based on his experience with the 24’er I’d think that an honest 6 MPG would be easily obtainable and maybe the MPG would get in the area 8 under the right conditions. That 8 MPG would lower the calculated fuel operating costs mentioned above even further!

I’ll not impinge on Tom’s intellectual property by posting any illustrations – I’ll leave than to Tom. But as I have told Tom privately – my schedule says I need to start building in about 18 months if I’m gonna have a boat ready for those long summers that are fast approaching, his 28’er is the most likely candidate that I have found to date that will allow me to tow the boat across the continent and taste the waters of various cruising grounds while being able to bring the boat home to my residence.

Best,

Leo

[charmc]

"But the boat should also be sea worthy enough that a bit of wave and wind blowing down one of the straits up north would not necessitate scurrying for an anchorage."
For several years I owned and cruised in a old Pacemaker 30', a bit bigger than you are speaking of, but a true Jersey sea skiff hull. The shallow v hull with a flat portion that you describe is more properly a Sea Bright skiff. The Jersey sea skiff had a fine, deep v entry, transitioning to a flat bottom aft, usually with round chines. Mine had a skeg, which protected the prop and rudder, and gave excellent directional stability in quartering and following seas. I did not build her, but I did do quite a bit of rebuilding, i.e. replacing planking that had rotted out over the years. While it was not easy, the work was "doable" by a definite amateur -- me.

As for seaworthiness, over the years I was caught offshore in a sudden summer squall on more than one occasion, but never worried about her seakeeping abilities. On July 4, 1976, after months of restoration, I took my family up to NY Harbor for OPSAIL 76. On the way back south, an onshore wind and outgoing tide created steep 6-7' seas. That night, several owners of fiberglass boats in the 40-50' range talked about how nasty and difficult the seas had been, with some passengers becoming ill. Our experience was a gentle rocking horse motion after finding the right speed, about 14 knots, just enough to stay on plane. At one point I noticed it was pretty quiet in the cockpit.... every one of my passengers had fallen asleep.

I found that, while it was possible to drive the hull to about 28 knots, that speed used a lot of fuel, and the hull would pound heavily in a chop. At 18-20 knots, however, fuel consumption was cut in half and she would knife through the waves.

For the cruising, seakeeping, fuel economy, and trailerability mentioned, something in the 22-24' range might be very good. The Sea Bright skiff bottom would facilitate pushing over a flat surface, or on rollers (rollers were used to move the early Sea Bright skiffs, used as lifeboats, across wide stretches of beach sand). The boat shown in the videos is definitely an easy-planing, and probably very economical design. My only concern is seaworthiness. By seaworthy I am speaking of big ocean swells. If the boat will be mainly used in lake and inshore coastal waters, that design would do very well.

I realize my descriptive terms are imprecise, and for that I apologize. I am not a marine engineer or NA; just a guy with 40+ years of experience operating small boats, sometimes (never by choice) in very rough waters. The challenge for boatbuilders in coastal New Jersey was always to build boats that could handle rough seas, but with a shallow draft and protection for the prop. 80% of the coastal estuary waters have a depth of less than
4', and a good portion of those waters are 2-3' deep. So jersey-built boats have good prop protection...or else!

[FAST FRED]

Great to get hands on feedback from someone to confirm the sea worthyness of this hull configuration.

Placing the boat on a trailer allows far larger range at low cost , as does the ability to container ship.

The Dalmation Coast , The Inside Passage to Alaska , the Med , Turkey,South Pacific and other really interesting cruising grounds are easily and inexpensively available.

Our use would be to cruise the an interesting area for 3 or 4 months in good weather , and ship her to the next years playground , safe and sound , away from sticky fingers in the Sea Land box.

Eventually we would bring her home and in our dotage trailer her to the many landlocked lakes and rivers here in the USA.

The 39 LOA will allow some extra goodies to be brought along with out killing performance. The biggest weight would be as on the old commuters , the drive package.
As diesel IS required (from a previous post where responders discussed the difficulty in obtaining gas) and for shipping , the price seems to be an engine weight 1500lbs plus tranny .
This is the range of genuine industrial engines , marinized that have NO electronic cam or injection , and no belt to drive a cam , as the auto conversions do.

For an out of the way cruiser I must be able to repair anything , and replacing a cylinder head because a cam belt broke , requires spares beyond what is rationally aboard.This leaves out the Styer or Yannmar.

Hopefully the LB ratio of such a slender vessel will allow the boat to operate in a very economical range , at good speed.

FF

[FAST FRED]

I found that, while it was possible to drive the hull to about 28 knots, that speed used a lot of fuel, and the hull would pound heavily in a chop. At 18-20 knots, however, fuel consumption was cut in half and she would knife through the waves.

When operating was there a HUMP or WALL in the boats performance?

In other words did the boat accelerate smoothly , each addition of throttle, giving a similar increase in speed?

Was there any point where LOTS of throttle was needed to get above a speed , and then normal operation?

Or where no matter what throttle was added , thats all she would go?

Thanks

FF

[charmc]

Fred,

I posted a reply to you earlier today, saw it added to the thread, now it's gone....strange.

OK, here goes again. There was a wall at the point of transition from displacement to plane speeds. Typical cruising scenario: Barely nudge the throttle for maneuvering away from the dock or anchorage area, a bit more in the channel, up to 7-8 knots. Stiil less than 1/4 throttle. To get on plane, apply 2/3 - 3/4 throttle; she'd plane in a few seconds. At that point she would accelerate rapidly without any more throttle, or I would throttle back to about 1/2 to maintain a comfortable and quiet cruise on plane of about 14-15 knots. Once I tried incremental throttle changes to get a feel for performance under all conditions. From 8 knots to 15, it took a lot more throttle to get more speed, with the bow up, stern down, and plowing along with ever larger waves at bow and stern.

I believe top speed was limited mainly by the prop. At 28 knots, the engine was nowhere near the redline, but more throttle made no difference in engine or boat speed, so a prop with a bit less pitch might have yielded a few knots more speed, at the cost of a lot more fuel use. The prop we had got her on plane easily, even with a heavy passenger load, so I never thought of changing.

Does this description answer your question, Fred?

[FAST FRED]

Delightfully answered! Thanks,

I wonder if the boat DISTURBER with the tunnel would do as well.

With such an unusual hull shape after the propeller will the usual speed prediction computer stuff actually work?

FF

[charmc]

Fred,

After reading the details on Disturber and the other boats in the article, I'm certain that design will give excellent performance with shallow water protection. As for your question on performance predicting software.....the main thing is to be sure all the design parameters are consistent with yours. Remember "garbage in, garbage out"?

That said, Penn Yan was successful for many years with their Tunnel drive, a similar concept. Although their tunnel was more rounded, I would guess there should be much similarity in performance curves. There should be plenty of data available on Penn Yan designs. Here's a typical P-Y tunnel drive.

[FAST FRED]

The usual tunnel drive is really different from the DISTURBER concept.

The usual tunnel is simply a grove in the hull that flairs out to accept the prop & rudder.

The Atkin design has the box keel in front of the prop , with the prop working in the water that flows around the box into the inverted V that is aft.

A look at the thumbnail (enlarged) will show the concept.

I wonder if the various Navy's of the world have a figured "better" box shape for their underwater appendages?

But then I'm not sure a Navy vessel will be running a SL of 3 , but there sure over 20K!

FF

[Geoh]

Fred
My cruising plans for next few years match yours BUT
I just bought this 1980 26' allweather boat ...only 31 or so made because nobody (except me) apparently is willing to go this slow...Seems to be everything you want except the 10k to 14k speed... www.allweatherboats.com

Geoh

[moTthediesel]

That Allweather is a robust looking boat, hull looks a lot like a motor lifeboat. I'm sure it will get you where you're going :cool:
moT

[Timm]

Maybe it's just me, but none of these boats look like true Jersey Sea Skiffs or Sea Bright Skiffs. Their keels are much too pronounced. In fact, the Jersey Speed Skiff had no built down keel. The box keel aided in launching the boat from the beach through the surf. The later power boats had smaller and smaller keels as the years passed, until boats built in the 50's and 60's had bottoms similar to a Lyman.

This isn't to say these designs aren't good, just that they always seemed to be a development based on some of the concepts incorporated in the Jersey shore boats. If anyone is interested in the history, check out a book called The Sea Bright Skiff and other Shore Boats by Peter J. Guthorn. Probably long out of print, but may be available in used book stores.

That being said, I love Robb White's interpretation of the Rescue Minor. I was always amazed at how light he could build his boats. I am sure if you calculated the structure it would probably fail all the typical criteria, but they seem to work anyway.

[SaltOntheBrain]

If your shaft angle is too great, the blades will only be generating thrust on the bottom half or each revolution as you get up to higher speeds, so the horizontal ( or nearly so) shaft of the sea bright skiff more than makes up for the appendage drag. As long as you're not trying to go too fast, anyway.

On the Penn Yann pocket tunnels, they were a compromise for shallower draft only. You lose planing surface and prop effeciency

[FAST FRED]

This is what one builder found, lifted from the net. FF

August 1, 2002
Yes, Atkin Was a Genius
By Robb White

We launched the Rescue Minor June 20th and she ran most marvelously. There was no ceremony to it. My wife and infant redheaded granddaughter and I just wheeled her down to Lake Lamonia about twelve miles down the road and untied the jackleg lines that held her on the trailer and she rolled off into the water.

The boat sits about an inch and a half down by the stem at rest but it is actually that she is up by the bow.... the toe of the stem is right at the water. It is because the boat is so light. I knew it would be like that and hoped it wouldn't be worse. When my wife and the baby got in up in the bow, she sat right down where she belonged. I hadn't brought the engine house, so, when we fired her up, she cackled pretty loud (about like a Kubota tractor) but didn't vibrate or shake the boat at all. While she was warming up, I checked all around to see how much exhaust water the little Shurflo diaphragm pump I adapted to run off the camshaft was giving (plenty) and what the oil pressure was and all. I think I was a little scared to put the power to the wheel and see what was what.

As soon as the propeller began to revolve, the stem picked up what felt like three inches and the boat began to move much faster than I would have expected from any planing boat at dead idle. Lake Lamonia is one of those lily pad lakes we have down here and there is only a narrow trail through the bonnets out to the clear water in the middle and I had fooled around looking at the engine and let us blow off so that we were heading for the lily pads but just a hint of rudder brought the idling boat right around. I have never seen an inboard boat turn like that.

There ain't no idle zone, so I ooched up on the throttle a little bit and the boat picked up speed just like a regular boat. I gave her a little more and she gave me a little more. I ran her on up and she ran on up. There was no perceptible rise to the bow at all and the wake never changed. The little engine smoothed out so that it was hard to detect any vibration at all when I put my hand on the cylinder head to see if she was warming up or not. The boat steered so stably that I could hold the tiller and walk all around the engine to check on my doings. Which, the copper tubing wrapped exhaust manifold ran cold and the inlet pipe from the keel-cooler stayed cold. There were no oil leaks and no hint of a diesel fuel stench or exhaust but I did have a damned tiny coolant leak from the plastic overflow reservoir. The outlaw graphite ceramic well pump shaft seal never gave a drop and the belt-drive transmission ran smooth as all get out.

Which, I hope I ain't ruined my credibility too bad. She ran 18.6 knots on the gps and that with the 10" pitch propeller that I put on there to make sure I didn't lug the engine while it was breaking in. That wheel let the engine run up to where the governor backed her off at 3,600 rpm. Me and Atkin think she 12-1/2" of pitch and I have that prop standing by ready to put on there. You know, I have the jackleg push-button prop nut and can change wheels by just reaching up under there with one hand. As an aside, that's a wonderful fig. I can take the propeller off a sailboat while she is luffed up in the mouth of the river. I wish I could lay claim to the invention, but it ain't nothing but something like a quick-disconnect like on a garden hose.

The boat ran most marvelously. I would have been satisfied with 12-1/2 knots (my speed) and a slightly tender feel (about like a deep "V") but the boat was so stable that my wife and I could hardly alter the running trim by both us, and the baby, sitting on the same side. She turns about level and, even then, weight distribution doesn't seem to affect the trim. I think the dynamics of the hull that control the wake hold the boat in a tight grip. It feels like it weighs about 10,000 pounds. There was never much wake at all but, like Alex's, there was a sporty looking rooster tail erupting about 8' astern. I have a little clamshell water pickup right behind the prop to give a little supplementary exhaust water at speed, and it is mighty effective (I could probably eliminate the engine-driven pump). The beautiful exhaust-water rainbow around the rooster tail made a most charming sight.

All my fears are put to rest. She ain't tippy at rest and she don't rise up by the bow and try to skitter off on that little pirogue she carries on her belly. I couldn't make her cavitate to save my life and the boat will turn, at speed, shorter than any outboard boat I ever had. I tried to make a wake to run back across so I could see what was what with that, but the boat doesn't make enough wake for a valid test. I ran across the wake of an aluminum butt head-skiff with a nine point nine that was much bigger than the wake of the Rescue Minor. I don't need no wake in no lake to tell me how she'll do in rough water. I know a sea-boat when I see one.

It is a wonderful boat and, as Alex said, "Atkin was a genius".

[BWD]

Chose this thread instead of the "box keel" now running in powerboats... Interesting topic. To get a better idea of the shape, I roughly modeled the lines from the "Grampus" in the motorboating article. Neither fine overall nor surface fairing done. Also a bit bigger dimensions, etc.
Here's the .fbm for anyone who wants to play with it. If I had time and software I'd scale, fair, etc. to try to learn more about this hull form. Does not look like a panacea, but it is interesting....

[Willallison]

BWD - what's a .fbm file? Nothing I have will open it...are you able to post in another format?

[Raggi_Thor]

Freeship :-)

[moTthediesel]

I tried but got a "not valid freeship file" message --

moT

[Raggi_Thor]

Sorry, I didn't try it, I just looked at the suffix and the icon...

[FAST FRED]

Sorry, I didn't try it, I just looked at the suffix and the icon...
__________________

Can you send it in PDF ?

FF

[BWD]

".FBM" is the freeship/delftship CAD file format. i authored it in delftship so the older program won't open it.

I don't have a lot of CAD ware and lack a good way to go FBM to pdf. Sorry. Anyway, delftship is free and fairly compact, if you want to play with it. From there you can easily export to serious CAD of your choice, thence to PDF....

Here's a picture from the model for illustrative purposes. As you can see it's not fair, the model's keel is merely a convenient curve (original is straight I think) and the keel chine is different. Still ok to look at, which is all I wanted to do in the 1st place....
Although if anyone builds one i would love to go for a ride!!

[fcfc]

I think you can find rescue minor lines there :
http://www.boat-links.com/images/RescueMinorLines.gif
BTW, on other forums, the displacement is said to be 840lbs.

[BWD]

ahh, now that looks like a better starting point than the magazine article!

[design.ho]

Hello Gentlemen,

Can anybody help me in finding a supplier who can supply me rescue boats of 6 person capacity? I am located in Sharjah, UAE and I can be contacted in the Tel No: +971 6 528 5345, email: aravindg@mis.ae.

Bye & Thanks
Aravind.G
Naval Architect
Engineering Division Structural Dept
Maritime Industrial Services, P.O.Box 4596
Sharjah UAE

[FAST FRED]

".FBM" is the freeship/delftship CAD file format. i authored it in delftship so the older program won't open it.

I don't have a lot of CAD ware and lack a good way to go FBM to pdf. Sorry. Anyway, delftship is free and fairly compact, if you want to play with it. From there you can easily export to serious CAD of your choice, thence to PDF....


With the unusual underwater shape aft , do you think the computer generated performance can be relied upon?

FF

[BWD]

To FF's qestion:

I think it could be done but the model needs attention first. The Motorboating article lines I used are muddy, so the model may be out 1/2 inch any old place, especially around the keel/tunnel.

Also, the rescue minor lines don't show as much vertical step to the keel chine, and I left this feature off my model, although it is not a model of RM, but an overscaled Grampus.

I believe these little steps may be important to the shallow water performance, generating vortices on longitudinal axes that will facilitate attached flow around the keel into the propwash and up into the inv. vee tunnel, affecting formation of the wake and reducing squat.

I think you would need a hydrodynamic modeling approach that could accurately include this type of flow, and prop wash interaction with it, if you want to look at a hull that has theses chines. Unlike conventional step chines, they stay immersed at speed.
Algorithms developed from flow around more conventional hulls might not be right for this one. I won't say more as I know very little of this type of software.

If I tried to build such a boat, I would start from RM lines in the .gif posted by fcfc, keeping in mind that it does not show much of a step to the keel chine. In tuning the design, you could "easily" add or subtract sheets of ply to the flat bottom to vary the degree of step, if needed.
I might also build with less hook and add central trim tabs to try to tune things, then wedge in hook as needed, as I think PAR suggested earlier in this thread or the related one.

[FAST FRED]

I have ordered the plans of "RIVER BELLE" from Mrs Atkins , as it is one of the last Sea Bright designed hulls.

Although RIVER BELLE has a deck house of huge size that would indeed condemn her to inshore use the lines plan is what I need.

The plan is to redraw the boat , using Herrishoffs STROLLER as a guide for the above water "look" and a slimmed down RIVER BELLE underbody.

I decided that a 1 inch to the ft model will assist in getting a rational interior .

I intend too tow the model alongside a small power boat , and install an electric motor only in the hull.

I should be able to observe any undesirable features as I power the scale model from the towing boat.

IF it works OK , A "Box Boat", probably of foam core or cold molded ply will be built.

Should be a great retirement cruising vessel, with all the ocean passages done by "Big Box Maru"in a shipping container.

Fingers crossed,

FF

[moTthediesel]

That's funny Fred, as I spent about an hour last night entering Atkin's River Belle lines into DELFTship as a background image. I'm following the tutorial the best I can, and I've made some progress, but I've got a long way to go yet. What I need is a copy of "DELFTship for Dummies". Anybody know where I can get one ;)

I'm an old dog I guess, but I'm still much more comfortable with clear pine splines and a #6 pencil --

When (!) I'm successful in getting the lines in there, I too plan to modify them above the W.L. -- Like you, I want to get the B.O.A. down to 7'6" or so. While I've seen LFH's "Stroller" and like it very much, I prefer the simplicity and extra interior volume of the raised deck style, so I'm thinking of something with a Blanchard or a Lake Union "Dreamboat" look.

I'd like to strip plank mine using Lindsay Lord's original method, crown/cove white pine (.40/bf here from Amish sawmills) sheathed inside and out with Dynel or Xynole in epoxy. Time comsuming? -- Hell yes! But v. light/strong and allowing for a much more "boaty" shape with lots of flare/flam in the bow and tumblehome in the stern.

The model idea is a good one, but you might think about making it bigger for hydro testing purposes. I don't think that a model 6' long would take twice as long to build as one 3', but the test data that it would yield might be that much more accurate.

moT

[FAST FRED]

"but the test data that it would yield might be that much more accurate."

The only TEST DATA I'm going to get will be from my Mark 1 Mod 2 set of Eyeballs , as we drag it alongside.

FF

[sal's Dad]

A couple comments:

There is another Atkin design, similar to River Belle, not in the catalogue. Alex Hadden built it a few years ago for a client, "Noble Cab" is cruising the Piscataqua. It was a difficult build, perhaps beyond even very skilled amateur capabilities. Reading between the lines of a recent conversation with Alex, maybe $400,000 to have one built to the same standard.

Before I thought about building or commisioning a big one, I'd ask for a ride.


It is my understanding that tow-testing of a tunnel-stern design will NOT provide meaningful data, the propeller pulling water into the tunnel is integral to its performance. This was discussed, perhaps on the AtkinBoats forum, a while back.

Sal's Dad

[kengrome]

The Tolman Seabright Skiff is a brand new inverted-vee tunnel-stern Seabright design. This boat employs a bottom that is very similar to Rescue Minor. This new boat is a dramatic departure from all the other Tolman Skiffs (Standard, Widebody and Jumbo) which are plain old v-bottoms their full length with sharper vee forward transitioning to shallower vee aft.

I'm building one of the new Tolman Seabright Skiffs now, but have only just gotten started and my camera is dead so I won't have any pictures to post for a while. I became interested in these boats when I read about Robb White's Rescue Minor. One of his comments intrigues me more than usual:

"I think the dynamics of the hull that control
the wake hold the boat in a tight grip. It feels
like it weighs about 10,000 pounds."

I think this is one of the keys to the unusual performance of these boats. Most planing power boats do not suck their bottoms down onto the sea surface, but it seems like this is exactly what Robb White was describing. If this is what's going on, it is no wonder why he also had this to say about his Rescue Minor:

"The boat was so stable that my wife and I could
hardly alter the running trim by both us, and the
baby, sitting on the same side. She turns about
level and, even then, weight distribution doesn't
seem to affect the trim."

My best guess is that while the boat is running its prop is creating underbody suction that keeps the boat securely 'attached' to the surface -- so effectively in fact that it behaves like a much larger or heavier boat. Nevertheless the boat does not squat because of the reverse curve of the after portion of the underbody. Instead the stern actually rises under more power, and this without the need for it to be wide like most outboard powered boats.

I also find this comment in the Grampus/Disturber article very interesting as well:

"The bow wave, at a certain designed speed, is
to a large extent trapped, and caused to run
smoothly into what amounts to twin tunnels, one
each side of the box keel."

I think this is the key to exceptional efficiency when these boats are run at their designed speeds. When a designer can trap and harness the energy of the boat's bow wave -- instead of letting that energy drift away from the boat -- it suggests to me that there is every reason to expect these boats to perform better than the average boat.

Personally I would like to design and build my own line of similar boats, some in the 15-17 foot size range, for even lower power requirements and even more affordability. Not every one wants or needs a 20+ foot boat, and for those who do not I believe a tunnel-stern Seabright skiff might be just the ticket -- especially for those of us who prefer moderate planing speeds.

[dick stave]

Where can we see the new Tolman seabright skiff? I am very interested to view this new design.

[kengrome]

Renn Tolman is working on the prototype and I'm building the first non-prototype from Renn's preliminary plans. Renn doesn't want people bugging him about the boat until he is ready to sell the plans, so this may be why no pix are available yet -- and my camera is broken so I cannot take and post pix myself (and I wouldn't without Renn's permission anyways).

In other words, I think this is one of those times when patience is going to be worth the wait.

I'm taking a chance that the boat will actually perform well by building one before Renn has finished and tested his prototype. Nevertheless I trust that William Atkin knew what he was doing when he designed his tunnel hull Seabright skiffs, and I trust Renn Tolman's preliminary plans (although I have found a couple of errors / omissions) ... so we shall see how this boat actually performs when it is finished.

Don't worry, I will post more info and some pix here as soon as I can.

[FAST FRED]

"My best guess is that while the boat is running its prop is creating underbody suction that keeps the boat securely 'attached' to the surface -- so effectively in fact that it behaves like a much larger or heavier boat. Nevertheless the boat does not squat because of the reverse curve of the after portion of the underbody. Instead the stern actually rises under more power, and this without the need for it to be wide like most outboard powered boats."

My reasoning for the flat,smooth ride would be almost opposite.

I think the hull rises aft from the water below being pressurized by the prop , lifting the aft area with enough force that any weight on the gunnels is unnoticed .
This could explain the flat level turns , lack of roll from beam waves and super smooth wake these boats leave.

The wake on the Shannon looks great , but the bow seems a very poor selection , blowing spray many feet into the air.
The much quicker Wallys don't have this spray hassle at low (20k ) speeds at all.

FF

[kengrome]

Sorry Fast Fred, I don't understand your reference to Shannon and Wallys, are these also Seabright skiffs?

Regarding your thoughts on the reasons why Robb White's Rescue Minor performed the way it did, I think your theory and mine may both be true:

The stern rises because of the water being pumped beneath it, that certainly makes sense. What also makes sense (to me anyways) is that there is no air beneath the hull when running because the propeller has forced it all out of the concave underbody of the boat, replacing it with water ...

Now that there is no air and only water under there, the hull cannot be easily moved up and down vertically -- because every upward movement will have to suck more water into the 'cavity' and every downward movement will have to force more water out of the cavity. Both of these actions are far more difficult with uncompressible water vs. easily compressible air, so the hull simply doesn't move up and down very much.

[FAST FRED]

The Shannon is a box keel style Shultz "invented".

The Wally is simply an example of a boat that makes very little spray forward , instead of the Shannon that sends huge sheets of water airborne.

FF

[SAQuestor]

From Working Watercraft of the World. A bit of info on Seabright Skiffs.

Link: http://farm1.static.flickr.com/250/455875226_c2f8e271c3_b.jpg

Link: http://farm1.static.flickr.com/193/455875230_2dc2a3ca45_b.jpg

Hope this helps the discussion.

Best,

Leo

[SAQuestor]

A Tolman Seabright. (http://fishyfish.com/renn_tolman/index.html)

Best,

Leo

[kengrome]

Hi Leo,

I disagree with the writer's conclusion that tank testing of Seabright Skiffs proves that they are 20-25 percent less efficient than other designs, and that their handling will suffer much like any boat that had a beer keg attached beneath the hull.

Personally I believe the engine needs to be running and the prop spinning for the hull bottom to function as it was designed -- which means utilizing the wave that comes off the box keel. When these boats are simply dragged through the water instead of running under their own power, the advantage of the tunnel stern is lost. Too bad the writer didn't understand this.

Thanks for the picture of Renn's Tolman Seabright Skiff prototype in his shop, I couldn't get any of his Seabright photos to load when I visited his page on the fishyfish.com web site so I thought someone removed them. Is that where you got this picture?

Note that the plans do NOT call for a transom cutout, Renn built his that way so he could use an outboard if he had to for some reason -- maybe a backup engine?

[SAQuestor]

{snippage}
Thanks for the picture of Renn's Tolman Seabright Skiff prototype in his shop, I couldn't get any of his Seabright photos to load when I visited his page on the fishyfish.com web site so I thought someone removed them. Is that where you got this picture?

Yep. FishyFish. Worked just fine in Firefox for me. Dunno about not loading in your browser.

Best,

Leo

[FAST FRED]

IF the assumption is correct that one of the "secrets" of the Atkin style box keel and negative deadrise aft is the acceleration of ALL the water under the hull, rather than just the propeller diameter, a good question would be can this be enhanced?

Ordinarily a large slow turning geared down prop gives the most thrust, but Atkin used 1-1 .

Sure some was prop diameter constraints to keep the boats beachable , and perhaps to keep costs down.

But could some of the value of the design be from the higher velocity prop stream , accelerating the rest of the water trapped aft to a higher thrust?

Have looked at steam injectors , and many have a resemblance to the aft Atkin shape .

What prop setup would maximize the entire water flow aft?

FF

[kengrome]

What prop setup would maximize the entire water flow aft?

I figure three of them, the big 10 inch prop in the center as designed, and two smaller props of perhaps 6 inches each -- one on each side maybe 6-12 inches forward of the aft end of the box keel.

I think the smaller side props would accelerate the water flow in each individual side tunnel before they merge to become one huge tunnel aft of the box keel. Then the larger main prop can "take over" and continue to blast the water aft.

Note that I am NOT thinking of building a three-propeller Seabright Skiff (not right now anyways) ... but it just so happens that I am building a Tolman Seabright Skiff at the moment, and I have a few pictures online now:

http://www.tolmanskiffs.com/seabright/