xx

system · July 27, 2004, 4:07pm

…

cerveza_fiesta · July 27, 2004, 6:09pm

That would probably be extremely difficult to calculate. Can ship design software take care of that? Something like autoship or maxsurf? That is my best guess

Respectfully,

-cerveza_fiesta

JohnB · July 27, 2004, 6:59pm

JayDee
Trace the underwater profile on to a sheet of cardboard, cut out and then balance it on the knife edge, which is at 90 deg to waterline. Where it balances is the CLR.[:-graduate]

Lester · July 28, 2004, 1:38am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by JayDee

The drop keep should in theory be placed at the Centre of Lateral Resistance (CLR)<hr height=“1” noshade id=“quote”></blockquote id=“quote”>
Hi John

I would guess that it would be more important to get the lead of the sailplan CE correct with respect to the overall CLR of the underwater body (fin included). That is, although it is probably reasonable to suggest that the fin should be placed somewhere around the CLR of the hull, once placed there, the sailing qualities of the result will be much more dependent upon the CLR of the result being the correct distance behind the CE of the sail plan. So dependent that I would not worry too much about the CLR of the hull alone, and would worry more about the CE of the sail plan, in order to have a guess at where the fin should go.

Lester Gilbert
http://www.iomclass.org/
http://www.onemetre.net/

Lester · July 28, 2004, 3:29am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by JayDee

No guessing allowed […] The sail plan is FIXED<hr height=“1” noshade id=“quote”></blockquote id=“quote”>
Hi John

Yes, I hope that is the point I was trying to make. If you need to put a fin in, position it relative to the fixed sail plan CE, rather than the hull CLR, you’ll have more chance of success. And you will have to guess as to the location of the fin, of course. I would imagine you will need to make allowances so that its position can be moved forward and aft a little until you can settle on the “final” position that seems to give you a boat with a balanced helm. The rule of thumb seems to be that you need to allow for a lead of somewhere between 2% and 5% of LOA.

Lester Gilbert
http://www.iomclass.org/
http://www.onemetre.net/

wgorgen · July 28, 2004, 5:12am

Hey John,

While I don’t want to belittle your quest, it seems to me that the position of the fin is far LESS critical on a scale schooner than it is on a top flite racing sloop. My reasoning for this is threefold.

The deeper draft of the remainder of the hull will tend to track straight. The sailing qualities of the full size boat from which the scale model is being built relied solely on that hull shape. The main reason for the bulb keel at all is to increase the righting monet, right? The lateral resistance added will just be a bonus.
You are (probably) not going to be racing in a tight one design fleet where fractions of a percent in performance make the difference between winning and loosing. You are more likey going to want the boat to perform well on various pointsa of sail rather than being optimized for upwind work. On a highly tuned racing boat, the balance of the boat is optimized for upwind balance at a particular heel which will sacrifice some of the sailing qualities at other heels and on other headings. With your schooner you will likely want to have a more balanced perfornace on all points of sail and for all wind conditions (I assume you are not going to have “B” and “C” rigs for your schooner…).
the sailplan of the schooner has a wider range of balance to the CE. By trimming the mizzen sail a very small amount, you can drastically move the CE aft. A small ease of the mizzen will result in a drastic shift forward. Given the low aspect ratio of the sail plan relative to the waterline length, you are not going to need to worry much about the lead of the sailplan because the CE will not shift far abeam as the boat heels (sorry Lester).

So given these caveats, I would suggest that JohnB’s method will get you close enough. You are essentially trusting that the full size boat was well balanced when you do this. But I would think that is a fair assumption.

I would think the more important thing to consider is the placement of the ballast fore/aft to get the boat to float on the correct waterline. Once you have gotten the ballast in the right spot, you are going to be fairly limited in where you can put the fin of the keel. I would say anywhere in that range is probably going to work pretty well.

Will Gorgen

Earl_Boebert · July 28, 2004, 5:55am

There are several tricks that can be used to help the sailing qualities of a model schooner:

The “lead centerboard.” This was used by the old-timers (1890s) to add external ballast. Cast a piece of lead in the shape of a centerboard as seen in this 1895 illustration. This looks much better than a fin and bulb in the water. You can also lengthen the slot, and put the attaching rod in a slot instead of a tube, to let you move the centerboard fore and aft for final hydrostatic trim.
If a gaffer, make the topsails removable so you can shorten sail in heavier air.
Use a porous sailcloth, like uncoated rip stop nylon, to reduce the amount of force the sails generate without changing their shape.

Cheers,

Earl

Download Attachment: [ LeadCB.gif](http://www.rcsailing.net/forum1/data/Earl Boebert/200472885538_LeadCB.gif)
36.5KB

Don · July 28, 2004, 7:56am

Jaydee
Is John’s method the same as the one you use. It sounds a little different and using the profile would account for the existing full keel.I’m going to float my schooner hull in a few minutes (got to have coffee first) and I will compare the push-pull and folded and balanced cardboard methods and let you know. I think everyones input is valid. Since we know the original mast(and therefore CE)location (I’m going to go out on a limb and assume that William Fife knew what he was doing)We should be able to approximate the CLR of the original hull. Will’s idea of balancing with sail trim makes me feel a lot more confident about ending up with a boat that handles nicely.

Thanks
Don
Vancouver Island

Don · July 28, 2004, 9:16am

O.K. It floated-that’s a good thing. The CLR was in the same spot using John’s method and the push the boat sideways in the water method. It’s nice when two different methods yield the same results. It took 5 1/2 lbs of tire weights to get it down to the waterline so allowing 1/2 to 1 lb for deck and rigging I should be able to use one of my US1M keel bulbs. Now I have to figure out how to plank the deck. I’m hoping to do end up with something like this.
http://www.fairlierestorations.com/index.htm

Go to Current Projects–Mariquita–Restoration About halfway down the page there is a picture of the aft deck- click on the little thumbnail for the fore deck. This may take a lot longer to build than the hull.

Thanks
Don
Vancouver Island

Don · July 28, 2004, 9:28am

Jaydee-When you planked your deck did you do it before or after you planked the hull? I’m concerned with sanding the deck planks with the bulwarks in the way.

Thanks
Don
Vancouver Island

Lester · July 28, 2004, 10:38am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by wgorgen

you are not going to need to worry much about the lead of the sailplan because the CE will not shift far abeam as the boat heels (sorry Lester)<hr height=“1” noshade id=“quote”></blockquote id=“quote”>
Hi Will

I am puzzled that I need to stand corrected. I believe all I said was that, for a balanced helm, it is relatively more important to have the rig CE appropriately positioned ahead of the (hull plus fin) CLR, than to have the fin at the position of the hull (canoe body) CLR. That none of these things need to be worried about in a model schooner is another issue.

Lester Gilbert
http://www.iomclass.org/
http://www.onemetre.net/

wgorgen · July 28, 2004, 11:50am

Hey Lester,

I was not really correcting you. I was simply pointing out that the “rule of thumb lead” of 2% to 5% was most likely not needed for a schooner. Because of the relatively short rig (relative to length) the CE of the sails does not shift as far abeam when the boat heels. So compensating for the tendancy to head up when the boat heels with lead is not needed for a schooner.

In addition, the extra sails involved in a scale schooner should allw you to trim your way out of balance problems with very fine trim adjustments further reducing any helm tendancies when heeled and thereby eliminating the need for designed in lead.

No offense was intended…

Will

Will Gorgen

JohnB · July 28, 2004, 12:36pm

There is another way besides the cardboard & push-pull method and thats using Simpson rule.

There’s a coulpe of download site somewhere, I have one on my laptop.

Lester · July 28, 2004, 2:02pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by wgorgen

compensating for the tendancy to head up when the boat heels with lead is not needed for a schooner<hr height=“1” noshade id=“quote”></blockquote id=“quote”>
Hi Will

One of the most interesting things to do with a canoe body is to artificially heel her (hang a little weight off one side, perhaps) and then give her way. She’ll immediately screw up to what would be weather if she were carrying sail. My understanding is that almost any kind of canoe body will do this (d’you remember how you were taught to steer your dinghy after they had taken your rudder away?), and hence some amount of lead is always needed when setting sail. This allows the wind pressure to blow the bows off the wind, counteracting the hull tendency to screw into wind when heeled.

I understand that, if you set the rig CE over the CLR, you would compensate for the missing lead by having the mizzen eased relative to the other sails. Correspondingly, if you set the rig CE too far ahead of the CLR, you would compensate by having the mizzen trimmed tight. But if you set the rig an “appropriate” distance forward of the CLR (or, in this case, fit a keel an appropriate distance aft of the CE) then you’d have a better chance of setting “realistic” sheeting angles on the mizzen when sailing on the wind. Good for scale appearances, perhaps.

Lester Gilbert
http://www.iomclass.org/
http://www.onemetre.net/

JohnB · July 28, 2004, 3:15pm

Don

5 1/2 lbs of tyre weights, there must be alot cars in Vancouer Island with unbalanced wheels[:-pirate][:-paperbag], I will keep looking in the newspapers for an alarmingly increase in vehicle accidents[:-bigeyes]

Don · July 28, 2004, 4:02pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by JohnB

Don

5 1/2 lbs of tyre weights, there must be alot cars in Vancouer Island with unbalanced wheels[:-pirate][:-paperbag], I will keep looking in the newspapers for an alarmingly increase in vehicle accidents[:-bigeyes]
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

Actually the increase has already happened. The Insurance Corp. of B.C. recently held a contest to see which town could reduce their accident rate.The average reduction for the province was 15%. Campbell River(my town)stayed the same. Honest,I bought the weights, really I did, really!!!

Thanks
Don
Vancouver Island

Don · July 28, 2004, 4:11pm

In messing with the CLR of the schooner this morning I noticed an interesting thing. After I had determined the CLR I looked at the plans to see where the masts would sit. Guess what, the mainmast sit exactly where it would sit if the boat was rigged as a sloop. I guess that because the mainsail hangs out over the stern and the bowsprit puts the jibs out over the bow it just leaves a hole in the middle that has to be filled with the foremast. I just thought it was interesting.

Thanks
Don
Vancouver Island

Don · July 28, 2004, 4:18pm

Jaydee
I was looking at your website and it looks like you built the deck first and then planked the hull. Is that right and if so can you tell me why? I’m looking at mine and in order to epoxy the underside of the deck I’m going to have to build the deck separate and attach it later.This is going to be tricky as the the deck follows the curved sheer and is also cambered a little bit. Maybe after I finish this I can get a job with Fairlie Restorations.(joke)

Thanks
Don
Vancouver Island

Don · July 28, 2004, 5:33pm

Jaydee
So is the foam still in there? If you remove the deck panel is the the deck still water tight?

Thanks
Don
Vancouver Island

Hoghappy · July 29, 2004, 12:57pm

Hey Guys…you ever consider making that drop keel like the one the Prince and the other square riggers over at www.modelsailingships.com
uses?

It has it advantages over the long bulb type keel. A much shallower draft is just one.

I don’t know what the formula is for deciding the thickness of the spacer between the keel and wieghted false keel is though. I suppose you would need to experiment with different thickness of spacers to get the ships heeling over qualities correct to scale.

Just a thought for pondering.

Robert

Always choose the lesser of the two weevils!