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  #136  
Old 04-26-2014, 12:50 PM
frank smith frank smith is offline
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GWA , none if this is rule of thumb stuff. These ratios mean nothing without numbers attached to them. Rather than think of them as sharpies, I would rather think of then as box section internally ballasted sailboats, and let numbers tell you where you have to be. The boat has to be wide enough to carry sail, narrow enough so that the ballast can be carried deep enough to provide self righting. and there has got to be enough freeboard to have a righting effect at large angles of heel. I think Bolger got it right with a deep hull, .75" to the foot rocker, 30% ballast ratio. low center of effort sail plan, and reasonable freeboard.

"Romp" is a different boat altogether.
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  #137  
Old 04-26-2014, 01:38 PM
goodwilltoall goodwilltoall is offline
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Well some of the "rules of thumb" or precedents can be what you mention, part of design is manipulating whats known to new ideas.

"wide enough to carry sail" that depends on what is the water plane area. I propose going for more of natural curve, 2.0' wide at both ends (+ balanced!!) (AS39 was about 2.5 wide fwd), keeping profile the same (this is the signature mark Bolger left and needed for dealing with wide ends in AS boats), extending to 47' overall with same beam (keeps self righting capability), hull height reduced to 5.5' (only because the pronounced rocker would reduce hdrm to less than sitting height towards the ends but would definitely try for 5.0' if possible when put to paper).

This would be a finer shape with lower CP ratio resulting in an easier to propel boat at slower speeds thus requiring less sail area. Keep in mind long boat are known to sometimes go above the 1.34 hull displacement speed because they go thru the water better but lets shoot for low power requirement of getting VL.9.

AS boats were about 77% LWL compared to LOA. Using these numbers you get about 7MPH which most any typical sailboat owner of a 33' or less with the same displacement would be pleased to achieve but still he would be incapable of venturing into shoals.

All this said because you need length to get there.

Btw, only AS29 has reasonable freeboard. Talk about Romp because of the narrow shape and 12" draft (or is it 18"?), there are nuggets in that design you can use to help understand other shallow draft boats.

Peace.
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  #138  
Old 04-26-2014, 02:32 PM
sharpii2 sharpii2 is offline
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Originally Posted by goodwilltoall View Post
Hull topsides kept to same height as as29 with deck house for standing hdrm at kitchen n bathrm only. Now to use some liberty, take that extra volume that is left over from cutting off 12" of freeboard and use it to add length (remember upto 6-1 l-b is the ideal ratio) keeping same profile, draft, and beam only downsides are a heavier boat and trying to figure out a comfortable design for the more awkward space but overall faster and much better sea boat.

Doing this most likely gives the boat a similar 180 degree recovery time since the added length increases instability upside down so you still get what Bolger claimed was the reason for adding high freeboard in the first place.
Added length for the same Beam and sectional area does no increase instability upside down.

To illustrate this point, let's imagine two three foot wide rafts.

Each raft is nothing more than a inclosed box with a 6.0 inch Draft.

The first raft is 6.0 ft long; the second one is 12 ft long.

The 12 ft raft, therefore has double the displacement of the 6.0 ft one.

Now, lets build a life guard tower, say 4.0 ft high, and put a 200 lb life guard on it.

Let's put one of these on each raft and have some malicious swimmers try to topple each raft, as the life guards snooze.

Which one do you think will flip the easiest?

Hopefully, you'd say the shorter one.

Because it has proportionately more top hamper. It has the same 200 lb life guard, as the longer boat, but half its displacement.

In the interest of fairness, let's put a second tower, complete with another 200 lb life guard, on the longer raft.

And let's go even further for fairness by assigning twice as many swimmers to topple it.

That should do the trick.

What seems to be missing from this discussion is the concept that ultimate stability always comes at the expense of initial stability. (except in the case of canting ballast)

If you want a boat that will recover from a 180 deg. capsize, it will automatically come with less initial stability, meaning it will be easier to knock down in the first place.

Granted, the tall sides, of the sharpies in question, provide a much better target for waves than the much lower sides of a much deeper boat, of the same Beam, Length, Displacement, and Sailing Draft. Also the base of the sail area is higher on the sharpies.

This is all true. But this subtracts from initial stability, not ultimate stability.

It is very possible for the deeper boat (of the same sailing Draft) to have less ultimate stability than the taller side sharpies. This is because its lower sides and up sloping bottom provide a poorer target for waves that might right it.

Also, it is likely to have a proportionately taller mast, which provides better dampening against self righting, initiated by wave hits.

When counting on the cabin as extra immersed buoyancy, during a capsize, one makes the implicit assumption that this cabin will not be breached in any way. If it is, it provides a handy water ballasted keel, to help keep the boat inverted.

Clearly, the deeper boat is the more seaworthy choice (certainly, while clawing off from a lee shore), but by how much depends more on its design than its inherent properties, compared to its higher sided competition.
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  #139  
Old 04-26-2014, 02:40 PM
bregalad bregalad is offline
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I built a Romp.
Romp has 18" draft. It also has an external lead keel of 2200 lbs.
The lead casting is 4" thick 10" wide and roughly 14' long. The wide. long centerboard slot passes through the lead. The center of gravity of the lead keel alone is 16" below the dwl.

Combined with the high freeboard and pronounced sheer she would have a strong tendency to right herself from a capsize.

A divorce got in the way of my ever sailing my Romp, but I've sailed on and with Jim Melcher's Alert. Romp, Manatee and Hogfish have proven themselves in shallow and deep water. It seems odd to speculatively ruminate over their behavior in different conditions while ignoring how they have actually performed over a long period of time and a lot of miles.

I am much less familiar with the AS designs so I'm hesitant to compare their real world performance to the Thames Barge model. I did design and build a 25' sharpie and sailed it up and down the Keys for about 2 years. Mine was designed and built with trailering and daysailing in mind. She was very light, but I think she would have been a fun boat on which to cruise the Bahamas, if you could stand the minimal accommodations.
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  #140  
Old 04-26-2014, 03:36 PM
goodwilltoall goodwilltoall is offline
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Well I'll use 2x4's on edge as example.
One 10' the other 5'.
If you push them over on a flat floor they probably require the same force proportionately to push on its side but say you had a gyrating floor simulating dynamic conditions the longer board seems that it would be more unstable. I also question if initial stability relates to ultimate stability, perhaps in some regards but to say its a direct relation I doubt that.

In BWOM chapter with the two AS designs you have the romp types right after (Ataraxia, Offshore Leeboarder, and Barn Owl), Barn Owl and OL have exactly 60% of overall hull height/beam and Ataraxia is close but with 10' beam it needs to be a little taller. Same story with Romp, just a little taller due to sitting hdrm requirement. Barn Owl section is supposed to be the epitome of the positive attributes of that design series.

Romp type boats in cross section are almost completely square except for the slight radius at chine, the ends are pointy at water line so it didn't require the extreme rocker above the waterline and proves Bolger did that to deal with the fat ends.

If you add that 4" deep external keel to the AS boats you get almost the same draft except that Romp needs to sit lower because of the rounded chine losing displacement. So this is speculative but their is plenty of recorded evidence to at least make some assumptions to say they will perform similarly.

Probably say go with pointy ends/more waterline rather than fat ends/short waterline (due to extreme rocker of the AS designs).
Now that I think about it, the OSTAR AS racer had a more pointy end and less rocker, same with josephbanks freighter.
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  #141  
Old 04-26-2014, 04:03 PM
goodwilltoall goodwilltoall is offline
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One more thought, if you do go with the finer shape and lower CP the overall displacement would not increase so drastically, with finer ends the total waterplane area could even stay the same.

Summary: fat ends require extreme rocker, light pointy ended sharpies can have them a hand width above the water at ends, with heavier displacement the forefoot can be immersed.
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  #142  
Old 04-26-2014, 05:35 PM
frank smith frank smith is offline
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Dont forget that while sailing the boat will be heeled. The waterline will be longer and the entrance will move towards the chine .
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  #143  
Old 04-26-2014, 06:13 PM
ImaginaryNumber ImaginaryNumber is offline
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Quote:
Originally Posted by goodwilltoall View Post
Well I'll use 2x4's on edge as example.
One 10' the other 5'.
If you push them over on a flat floor they probably require the same force proportionately to push on its side but say you had a gyrating floor simulating dynamic conditions the longer board seems that it would be more unstable.
I would hazard a guess that when lying flat in the water a 10' 2x4 will be more stable than a 5' 2x4.

Quote:
...Probably say go with pointy ends/more waterline rather than fat ends/short waterline (due to extreme rocker of the AS designs)...
As Frank Smith just pointed out, the AS-xx series only have a short waterline when upright, which facilitates tacking. However, when heeled their waterline lengthens, resulting in a surprisingly fast boat.
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  #144  
Old 04-28-2014, 06:03 AM
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Angélique Angélique is offline
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All contributors, this helped my understanding, thanks for the detailed comments and explanation on the upside down stability issue
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  #145  
Old 04-28-2014, 07:01 AM
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Angélique Angélique is offline
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Originally Posted by goodwilltoall View Post

All other things equal, during a 90 degree knockdown the tall sides of as39 (6'-0") will right slower than as29 (5'-0"). In an 180 degree rollover as39 shape will be more unstable and aright quicker. Taller sides will make the boat more prone to knockdown in the first place.

At waterline as39 (37.0' loa;7400#) is almost identical to as29 (29.5' loa; 11,000#). They both have same profile except that as39 is longer, same depth, same beam. They are pretty much the same boat other than length. So here goes another example of the superiority of ark proportions.

Bolger could have maintained the 5' hull height as as29 (this almost exactly matches the ark dimensions of hull height being 60% of overall beam width which would have been 4.7' but had to go to 5.0' for at least seating hdrm) this would have made as39 a better sea boat but he chose other reasons in favor of comfort for the added freeboard. I think in the book he said ultimately safer because as I mention above it more quickly comes back from 180 degree rollover but this is the wrong reason to do it since this way you get more rolling from both waves and wind resulting in a harsher ride, this is a direct result of the heavier/taller topsides.

Out of almost 700 designs, Bolgerites will recall him saying Manatee/Romp (the ultimate in this design series was Barn Owl with wide bow "almost" like a barge/scow) was the most seaworthy boat he ever designed. Very close proportions to the above boats in beam, draft, freeboard, length. Yes, it was rounded at the chine and with flare at fwd section rather than wide upswept water plane for buoyancy however I can see these two type of boats acting alike in similar conditions as long as freeboard is kept low.
This is very tiresome and uncomfortable and since fatigue of the crew is the biggest killer of seaworthy boats this is not only about comfort but it's also a safety issue that should be taken into consideration...

P.S. -- Just recalled, Sailor Alan mentioned the fatigue issue here...
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. . . . The high sided, flat(ish) bottom boats are extremely seaworthy, but need intelligence at the helm. They will indeed snap back up from a knockdown, and definitely slide sideways when hit by a wave. BUT, one needs to reef early and often, especially at night. Their motion can be very 'quick' and therefore very tiring for the crew. Its often the crew which fails first, and many of the historic ocean voyages in small boats were really just endurance tests for the sailor . . . .
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  #146  
Old 04-28-2014, 12:32 PM
frank smith frank smith is offline
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I think that if the boat is kept narrow and deep enough, the roll rate should not be to bad. The box form itself has good damping.
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  #147  
Old 04-28-2014, 04:20 PM
sharpii2 sharpii2 is offline
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Originally Posted by goodwilltoall View Post
... I also question if initial stability relates to ultimate stability, perhaps in some regards but to say its a direct relation I doubt that...
They are indeed linked.

By "Initial Stability" (IS), I mean righting moments up to 20 deg. of heel.

This righting moment comes from buoyancy shift. The shallower a Hull Section is, in relation to its Beam, the greater this buoyancy shift is going to be. Center of Gravity (CG) plays a part in this as well. So a higher CG is going to mean less IS, because, as the boat heels, the CG also moves to the leeward side. So, if you made two sharpies, one with a high deck and one with a low deck, and gave them both generous internal ballast, the one with the low deck will have more IS than the one with the high deck.

But the one with the high deck will be more likely to recover from a an extreme capsize, for reasons I explained in earlier posts on this thread.
It has an added advantage of at least some of its payload acting as self righting ballast as well.

Of course, you could take the low sided sharpie and add a deep ballast keel, in exchange for the internal ballast, and keep the original IS and add more Ultimate Stability (US).

On paper, that looks fine. The problem is that the external keel adds buoyancy below the hull (though miniscule compared to its weight) and, unless it is very deep, the amount of ballast has to be quite large to meet its self righting function.

This subtracts from the payload of the boat, unless a deeper section is drawn. The deeper section, of course, means less buoyancy shift at low angles of Heel, hence less IS.

The trade off between IS and US can be quite subtle, but it is always there. It has bedeviled rating rules committees for over a century.

A longer, sharper, boat, of the same displacement and Water Plane Area (WPA), trades some IS for a longer at rest Water Line (WL).
The sharper ends subtract from the Average Beam, thus reducing the amount of buoyancy shift.

When this boat starts to heel, if it has shallow sections, some of the bow and maybe even some of the stern comes out of the water, shortening the WL right at the time a longer one would be most useful (when there's plenty of wind).

Attached below, is an extreme reaction of mine to this phenomena.

The scow shown here has quarter butts that are considerably longer than its WL.
Attached Thumbnails
Hogfish Maximus - 44ish sailing sharpie?-jb-10p.png  
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  #148  
Old 05-31-2014, 08:50 AM
goodwilltoall goodwilltoall is offline
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There are two drawing with the PDF file click to second one.

Decided to put it to paper and this is what I had in mind for the AS design with a 7'-10" beam. In the drawing there is a note for raising freeboard 3" at bow, this is for assuring sitting hdrm at double berth and it also brings it upto same height at bow as AS29.

If an additional working desk is desired such as on the original LM it would be put where the passage way is to aft storage area which would also require the aft sheer to be raised 3".

Design is symmetrical and raised hull above WL according to width of the ends (as previously mentioned, for wider ends more rocker and for pointy ends just a hair above WL). Did away with mast tabernacle well as it would seem to troublesome holding water and getting access to clean out but do have a well for anchor gear. I would also stay the masts.

Draft is an additional 4" more than originals for bigger rudder area (5.3sf below WL)
Attached Files
File Type: pdf scan.pdf (432.7 KB, 165 views)
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  #149  
Old 05-31-2014, 01:10 PM
Tanton Tanton is offline
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Sharpie.

In Bolger's footstep.
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Hogfish Maximus - 44ish sailing sharpie?-984ga.jpg  Hogfish Maximus - 44ish sailing sharpie?-984sail.jpg  
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  #150  
Old 05-31-2014, 07:15 PM
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Sailor Alan Sailor Alan is offline
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Originally Posted by goodwilltoall View Post
There are two drawing with the PDF file
And George Beuhler. http://www.georgebuehler.com/Wunderberg.html
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