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  #121  
Old 04-24-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

If I have understood the objective is to maintain the boat's looks and make give it a modern hull, rig and performance.

If so maybe it should be adequate to maintain the wooden hull, but in a modern way, for instance strip planking.

The use of that building technique will allow a substantial gain in weight that adds to the less weigh needed as ballast since the boat is lighter and the ballast is lower.

That means that if the original hull lines are maintained the boat will not have the same waterline and will seat much higher on the water.

The question is: It does not make sense to modify the hull shape to the new reality (a lot less weight) as a way to maintain the original waterline and improve performance?
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Last edited by PCP; 04-24-2013 at 06:12 PM.
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  #122  
Old 04-24-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Boy, this is way too complicated for me.
I think a cutter, ketch or sloop rig would work fine on this hull guven it was designed properly. There is nothing about those three rigs that dictates hull design. ou just have to get the keel in the right place relative to the rig and you should be fine. I know I could do it. Again.

PCP:
I agree with you and I tried to indicate in an earlier post today that I am leaning of Jeff to make some major changes in the hull form. Jeff's taking it one step at a time. I think he may actually have a real job. I do. Let's see where he goes next. I have passede along my suggestions.
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  #123  
Old 04-24-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by PCP View Post
Brent, I don't pretend to know that much but some of those boats are designed by some of the best NA around. They utilize CFD to study the hulls keels and rudders and I am sure that they are like that because it is the way they work better.

Regarding the canting of the keel what is the point to have a 25º angle on a boat that sails with 15/17º of heel? it seems to me that the better efficiency would be obtained with a vertical foil in what regards sailing heel.

Regarding the keels having a small attachment you are probably imagining that each one is fixed to the hull. In the RM case (and in many other boats with skinny keels) they are both connected to the same steel structure inside the boat that distributes the efforts by the hull.

Regarding beamy hulls reducing ultimate stability I don't know what you mean. That depends basically to how lower is the CG and normally those boats have considerable drafts a god B/D and bulbed keels. That gives them a good AVS and a very good reserve stability at 90º.

Yes, when inverted they have a big inverted stability but again how easily they return to its feet depends on the CG. It is convenient not to forgot that to the big inverted stability corresponds a much bigger positive stability, much bigger than in a narrow boat. In the end, besides a good AVS and a good reserve stability what is important is the proportion between the positive and inverted stability (a much bigger positive stability).

Regarding that thing about the anchor being wrapped about the keel, those boats are popular in France, there are hundreds of them and I never heard complaints about that neither anybody referring that as a problem with that kind of keels.

Regards

Paulo
Paulo
Make yourself a model, a flat piece of wood with keels like these will do. Then tie a line to the bow take it between the keels, then to one side. Picture a boat in this position in a strong beam wind, and see if laying broadside to the wind and swell, with the line under the full load of the wind and sea abeam, will allow you to get the rode off the keel. I have no doubt that tank tests show this type of keel to sail well, but tank tests dont ask the question of how you get a fouled anchor rode off one when you are abeam to a strong wind and sea on a dark night. Numbers and math dont answer that question, and a lot more practical questions about actually using the boat.
My first boat was a Pipe Dream designed by Francis Kinny and tank tested inthe Davidson lab in New York, the tank where all the US Americas cup boats were tested. She had a short keel with rudder attached. With zero sailing expereince, I looked at the rudder and thought " Maybe a rudder on a skeg six feet further aft would be better." Then I thought " Gee, I have no expereince so I beter do what the designer drew." Off the wind the boat was almost uncontrolable in strong winds,an absoluite abortion of a design screwup, so when I got to New Zealand, I replaced the rudder with a separate rudder six feet further aft on a skeg, just as I had originally thought, with zero experience.. The improvement was huge. That completely blew my confidence in the infalibility of world reknown "Experts."
Einstien said "Wisdom doesn't come from studying , Wisdom comes form showing up for life."
Very few boats sail in strong winds at less than 15 degrees of heel.
Angus Primrose, while crossing the Atlantic in one of his very beamy designs was capsized, and was dismayed at how long she took to right herself. He later did some calculations and found that even a slight reduction in beam made a huge improvement in ultimate stability.
Again, boats staying capsized was never a problem, before excessive beam became the norm.
A beach ball with a high CG and a tiny ballast ratio has a very high ultimate stability. A wide raft with a very high ballast ratio and low CG will have a very poor ultimate stabilty. Thousands of pounds of buoyancy in a wheelhouse will be the equivalent of adding far more weight in the keel, in the inverted position, when it comes to ultimate stability. The more the midships section resembles a beach ball (Trunk cabin with high camber) the higher it's ultimate stability. The more it resembles a raft, the lower it's ultimate stability. The calculations they use dont take this into account, making them dead wrong.
Any accountant will tell you that, when adding up numbers ,get one wrong, and everything you do from that point on is wrong. Miss a huge factor like buoyancy in deck shape and structures, and everything you calculate from that point on is wrong.
Skinny keels fold over, regardless of what you put inside. Perhaps these boats are designed to the standard plastic boat standards, where they are simply expected to break up if they hit anything.
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Last edited by Brent Swain; 04-24-2013 at 08:15 PM.
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  #124  
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Brent Swain View Post
Paulo
...
Angus Primrose, while crossing the Atlantic in one of his very beamy designs was capsized, and was dismayed at how long she took to right herself. He later did some calculations and found that even a slight reduction in beam made a huge improvement in ultimate stability.
Again, boats staying capsized was never a problem, before excessive beam became the norm.
...
Brent, there are well designed boats and badly designed boats. These days very few are badly designed. Regarding beamy boats has I said, they have more positive stability (are harder to capsize) and when capsized require more energy to be re-righted. In the end it is all about the proportion between positive and negative stability.

Regarding ultimate stability considering that is the stability that is not used for sailing till the AVS point, you are wrong to assume that beamy boats have necessarily a bad reserve stability. Many have a a better one than narrower boats. I know, I have seen and studied many stability curves trying to understand that. In fact 10 years ago I used to thought like you.

Just to point you in the right direction have a look at this video:



This is a 40class solo racer, the boat that had inspired the hull of the RM, except that this one is a lot beamier. For 12m of length has 4.5m of beam.

You can see that he can recover from 180º without the help of waves just changing the water in his ballast. Obviously he cannot do that if the low CG, in this case high is not helping a lot. In fact these boats have typically an AVS around 130º and have a huge reserve stability. That boat at 90º is making more force (regarding its weight) to get back to his feet than any cruiser I now off and I know a lot of them.

Regards

Paulo
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  #125  
Old 04-25-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Might be helpful in this discussion to use some real numbers and try to get away from theoretical and philosophical issues. Define an L/B that you like or don't like. Bracket some questionable numbers. Define some of the variables and there are a hell of a lot of them.

Paulo is correct, obviously. There are good heavy boats and good light boats. There are also bad heavy boats and bad light boats. I'd like to see the more specifics enter this discussion. I like to treat each boat individually.
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  #126  
Old 04-25-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by hellosailor View Post
Jeff- From #90, the context is :
"Considering, the suggestions to consider retaining either a Cutter or Ketch rig, The while both rigs have virtues in some applications, both would be inconsistent with the hull and keel as it is evolving. It is important to go back to the decision loop thought process. Both cutters and ketches are at their best in boats with lots of drag for their stability."

I read that as "drag for their stability" but I think you are meaning the rigs are better off for the stability they create in boats that have lots of drag or inertia and as such are slow to accelerate?
Ah, Now I see where you are coming from. That was not the most clearly written sentence on my part. What I was trying to say, was that cutters and ketches are best on boats which have a lot of drag and which also lack adequate stability to allow an efficient (lift to drag) sail plan to be used. Efficient sail plans tend to be taller and have a higher vertical center of effort. When you talk about a boat with a lot of drag, it takes a lot of sail area to over come that drag. And if you have a lot of sail area and its in a sail plan with a higher vertical center of effort, it requires a lot of stability to be able to use that additional sail area. Ketches and to a lesser extent cutters tend to spread thier sail area out more horizonatally so they generate less heeling moment for thier area, but of course they cannot point as high as a more efficient rig.

My poorly written sentence was short-hand for all that. It was clear in my mind but of course, only the clarvoyiants on the forum who were reading this knew what the heck I was thinking.

Jeff
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  #127  
Old 04-25-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

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Might be helpful in this discussion to use some real numbers and try to get away from theoretical and philosophical issues. Define an L/B that you like or don't like. Bracket some questionable numbers. Define some of the variables and there are a hell of a lot of them.

Paulo is correct, obviously. There are good heavy boats and good light boats. There are also bad heavy boats and bad light boats. I'd like to see the more specifics enter this discussion. I like to treat each boat individually.
Because of the bad heavy boats and/or full disp, people have chosen to say ALL heavy and/or full keels boats are horrible from a performance point of view. For a long time I used my boat to dissuade such notions then I finally realized my boat was an exception to that "rule".
The poor handling and windward ability of the original design of my boat was overcome with a subtle rig change. The type of hull is actually based on a New England fish schooner, but a 30' hull just isn't practical for a schooner rig. The rig on the boat is a high aspect ratio and the hull is designed for a rig with a center of effort fairly far aft (big main fractional fore triangle), a ketch rig would lower the center of effort but would move the center of effort ahead of the what the hull was designed for.
It doesn't take much to get the boat to hull speed and it still moves nicely in light air, the most an improvement in hull design could do is improve very light air performance or maybe reduce the amount of sail area necessary to achieve the same thing it does now (good for handicapping, but I don't do racing). You have already pointed out how you can see this hull would do nicely in light and moderate wind. I have learned from previous owners of my boat and others with the same hull that when weather gets dicey it is a good "sea boat", you did say there might be a problem if I was sailing without reduced sail in weather where I should have reduced sail anyway.
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Re: Bob Perry's take on Wolfenzee's dream boat

Wolf:
If you went to a ketch rig you would almost certainly more the center of pressure aft not forward. I'm not proposing a ketch at all. I like the rig Jeff has sketched up now. I'm not in favor of split rigs on boats this size.

You are dead wrong saying, "the most an improvement in hull design could do is improve very light air performance or maybe reduce the amount of sail area necessary to achieve the same thing it does now ". It's a bit silly to ignore all the improvement in hull desiign that that last 50 years have given us. I could not stay in business if I ignored them.

Jeff and I will proceed with the project and do what we think wil work well while retaining tha character of your boat. No fun in this for Jeff and me if we are going to be anchored in the past. Your boat is a skinny boat and benefits from that lack of beam. But other than that the shape is a pure antique. But it's a nice antique, I like it and I understand why you like it. But this is 2013. Isn't it?
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  #129  
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by bobperry View Post
Wolf:
If you went to a ketch rig you would almost certainly more the center of pressure aft not forward. I'm not proposing a ketch at all. I like the rig Jeff has sketched up now. I'm not in favor of split rigs on boats this size.

You are dead wrong saying, "the most an improvement in hull design could do is improve very light air performance or maybe reduce the amount of sail area necessary to achieve the same thing it does now ". It's a bit silly to ignore all the improvement in hull desiign that that last 50 years have given us. I could not stay in business if I ignored them.

Jeff and I will proceed with the project and do what we think wil work well while retaining tha character of your boat. No fun in this for Jeff and me if we are going to be anchored in the past. Your boat is a skinny boat and benefits from that lack of beam. But other than that the shape is a pure antique. But it's a nice antique, I like it and I understand why you like it. But this is 2013. Isn't it?
I am also not a fan of split rigs, or at least not for anything under 40'. I would not ignore improvements in hull design, but by the same token too many people in too many things only look at "improvements" and are lead to believe everything prior to them must be bad. A better way to describe what I was trying to say is the improvements suggested are more extreme than the improvements in performance. That and flat out performance it not the only feature of hull design, just the easiest one to sell to a culture whose mindset revolves around speed. The biggest drawback of my boat is in accommodations, it is fairly evident that the overall design was based on something alot bigger. An yes she is an antique, but a nice balance of form and function....not what one of these "wooden boat snobs" over here have which perform best in a slip at a boat show. My boat was designed as a single handed ocean cruiser.
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Re: Bob Perry's take on Wolfenzee's dream boat

Wolf:
Good. We can proceed.
Yep, as pretty as that old hull shape is it does put a lot of displ down where you can't use it for anything other than canned goods or wine. If we increase beam and reduce deadrise we can give you a lot more usable volume for accomodations while increasing the cabin sole area greatly. At the same time we can increase initial stability and make the boat sail better on all points of sail. We can make the boat do your bidding around the dock under power too.
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