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Old 17-04-2012, 15:31   #1
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Piver conversion daggers or keel ?

I have a 45ft. piver built by kettenburg boats its 1965 pilothouse ketch. Its heavy and makes a very comfortable cruiser.It has two small fins in the middle of the amas. I have tried different sail combinations. It sails terrable and will turn 90 degrees to the wind and just sit there stalled and no matter what you do it wont come out of it besides start the motor and then reset everything and fight to keep it that way. Ive heard people fix this with keels which I disagree and dont want to do. I read about this in book designs and the easiest fix that does work is Daggerboards. I pushed the side of the boat and center of lateral resistance is three feet behind the main mast. With a big main and headsail center of effort I would say is probably three feet in front of the mast. Or at least just in front of the mast. There is a forward hatch in the amas just in front of the crossbeam and the hulls are very verticle in this area,not much curve inward. The deck to keel about four feet. I believe I could install a board here easily in both amas and be very strong and work great. Board would be at least 8 feet long. 16 inches wide between ribs. This would line up the CLR with CE. It would not change my depth except boards down and easy to repair. ANY THOUGHTS WOULD BE APPRECIATED.
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Old 17-04-2012, 16:31   #2
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Re: Piver conversion daggers or keel ?

The first Questions are do you have a fixed prop or a folding one? Second question is the bottom clean?
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Old 17-04-2012, 17:06   #3
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Re: Piver conversion daggers or keel ?

Fixed Prop three blade and I scrape it clean everytime I sail. Im hualing out soon for new bottom and hopefully a good conversion to fix. Thanks
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Old 17-04-2012, 17:38   #4
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Re: Piver conversion daggers or keel ?

The fixed blade prop is what is causing the problems, install a folder before you spend on the conversion. Most likely there are barnacles on the very bottoms as well if you're having to scrape instead of scrub. Bottom paint should be on the list before daggers too.. When you do the conversion the CLR and CE should be in line with each other. In theory about where the float fins are.
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Old 17-04-2012, 17:44   #5
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Re: Piver conversion daggers or keel ?

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Originally Posted by Cavalier MK2 View Post
The fixed blade prop is what is causing the problems, install a folder before you spend on the conversion. Most likely there are barnacles on the very bottoms as well if you're having to scrape instead of scrub. Bottom paint should be on the list before daggers too.. When you do the conversion the CLR and CE should be in line with each other. In theory about where the float fins are.
Agree. Folding props and clean bottom. before any big mods like dagger boards
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Old 17-04-2012, 18:51   #6
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Re: Piver conversion daggers or keel ?

And lighten ship, a tri shouldn't be heavy so clean out all the storage areas. Pivers can sail given the chance.
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Old 17-04-2012, 19:57   #7
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Re: Piver conversion daggers or keel ?

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Originally Posted by Richard Ellison View Post
I have a 45ft. piver built by kettenburg boats its 1965 pilothouse ketch. Its heavy and makes a very comfortable cruiser.It has two small fins in the middle of the amas. I have tried different sail combinations. It sails terrable and will turn 90 degrees to the wind and just sit there stalled and no matter what you do it wont come out of it besides start the motor and then reset everything and fight to keep it that way. Ive heard people fix this with keels which I disagree and dont want to do. I read about this in book designs and the easiest fix that does work is Daggerboards. I pushed the side of the boat and center of lateral resistance is three feet behind the main mast. With a big main and headsail center of effort I would say is probably three feet in front of the mast. Or at least just in front of the mast. There is a forward hatch in the amas just in front of the crossbeam and the hulls are very verticle in this area,not much curve inward. The deck to keel about four feet. I believe I could install a board here easily in both amas and be very strong and work great. Board would be at least 8 feet long. 16 inches wide between ribs. This would line up the CLR with CE. It would not change my depth except boards down and easy to repair. ANY THOUGHTS WOULD BE APPRECIATED.
Thanks you guys for all the input.
It was also suggested since I live heavy in this boat is to add a layer of styrofoam to the bottom then a layer of ply and glass to add more flotation. Also a longer rudder.
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Old 17-04-2012, 20:12   #8
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Re: Piver conversion daggers or keel ?

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When you do the conversion the CLR and CE should be in line with each other. In theory about where the float fins are.


Don't know much about multi design, but I do know a lot about mono design. The distance between the CLR and the CE is called Lead, and it is what determines the amount of weather helm a boat has. No designer would draw a mono with CLR and CE in line, it just isn't done. You need some lead to develop weather helm or the boat will end up with lee helm instead, a bad thing. Do some research. If this were true most boats keels would be substantially further forward.
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Old 17-04-2012, 21:12   #9
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Re: Piver conversion daggers or keel ?

Your right, trimarans are much different from monohulls, . You need to do some multihull research. Find some books and start looking at plans. Chris White's book is a good place to start. Derek Harvey's book "Multihulls for Cruising and Racing" is another. Older books like Harris's "Racing and Cruising Trimarans" and Rob James "Multihulls Offshore" have much relevant information. Because they don't heel like a monohull they don't need the lead. Complicated things do happen and ama (float) shape, length and beam are all interrelated. Much less lead is required, some boats need a little, others none. Cats are simple by comparison to both......
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Old 17-04-2012, 22:40   #10
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Re: Piver conversion daggers or keel ?

Thanks I will check more into it but the multi books I have read say just do Dagger boards. There seems to be a lot of variables but no real scientific proof for any. Thanks
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Old 17-04-2012, 23:43   #11
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Re: Piver conversion daggers or keel ?

The sceince is proven by how well your boat balances and sails. There is a lot of new learning to do when coming from the world of the heavy monohull cruiser. A trimaran gets its safety from being light and has to be treated like an aircraft not a merchant ship. They sail on the waves, not in them.
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Old 18-04-2012, 08:36   #12
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Re: Piver conversion daggers or keel ?

Here are the basics of lead....As a monohull heels the CE of the sails move to leeward of the hull. The rig drive and hull drag create a turning moment that turns the monohull to windward. to counter act this the CLR is placed aft of the CE of the sails-Lead.
A multihull heels much less but the boat's displacement transfers to the lee hull (catamaran) or ama (trimaran). The center of resistance to forward motion also moves leeward outboard of the drive of the sails creating turning moment to leeward- opposite a monohull. To counter act this the CLR is place at or forward of the CE.
This is the basic idea but there are other factors such as bow shapes which can add area forward that have to be considered as well as the huge influence sail shapes have on the CE. Construction of trunks and their installation also have to be top notch.
Arther Piver wrote 3 books that are entertaining and cover his designs well, they are available used for very little money and are recommended for anyone owning one of his designs. When he went to locate the CLR they clamped boards to the sides of the hull until they found the best place for the ama fins with the designed rig. A common problem they had with builders back in the day was the installation of inboards with fixed props which acted as a brake and shifted the CLR. Less than clean bottoms are like ice on airplane wings- they can keep you from flying!
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Old 18-04-2012, 09:33   #13
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Re: Piver conversion daggers or keel ?

After you follow the suggestions above; I agree about getting the boat light. After completing the initial suggestions, I'd get her empty, very little water and fuel, empty, and take her out, see what you have. You probably will need to do this several times. This would be my assessment sail weight. If I was pleased with this results then I would begin to load the boat carefully and monitor the changes; when sailing performance began to suffer you will know you have reached payload.

If after the initial "empty weight" sailing evaluations you believe a board would make a difference I would consider a swing board located in the main hull, with a box built under the long salon bench. Boards in the main hull do not need to be centered or another way to look at it is they can be off center and still be effective. However if you can figure a way for a dagger box in the main hull that might even be better.

Take a look at what Chris White did in the Hammerhead 54 Chris White Designs

Shannon has put a dagger boards port and starboard of their new 53HPS monohull http://www.shannonyachts.com/sail53specs.html

I think this would also be less stressful on the boat as compared to the boards in the amas.



If I was going to add flotation I would think about only adding it to the amas and use something like this:

http://www.fibreglast.com/product/2_Lb_Polyurethane_Mix_and_Pour_Foam_24_25/Foam


You would need some type of internal decking at or perhaps just above the waterline in the amas to pour the foam through so it would form and contour to the hull shape below; the decking would be the upper part of the mold and contain the foam in place.

I hope you will keep us informed and let us know what you do and the results.

Good Luck
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Old 19-04-2012, 09:23   #14
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Re: Piver conversion daggers or keel ?

I'm not sure Shannon had much to patent, the Oceanic Cat had fins that didn't extend beyond the keel a loooong time ago, interesting dagger adaption though, the forward rake will cut down on ventilation as the boat heels and the board entry moves above the waterline....
Pivers are more like a cruising cat in that all the hulls stay in contact with the water for less of a change in balance. A tri with the amas at or above the waterline is going to have more complicated interactions. It heels more so there is some of the same thing going on as a monohull but in performance situations may even fly its main hull. Getting good control through all the transitions is a balancing act.
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Old 20-04-2012, 07:55   #15
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Re: Piver conversion daggers or keel ?

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Pivers are more like a cruising cat in that all the hulls stay in contact with the water for less of a change in balance.
Of course this means more drag since there are 3 hulls in the water instead of two for either the cat or the modern tris. But the boats are still great cruisers.
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