Twin rudders – how much smaller than a single rudder?

[kenjamin]

Yo fellow forumites,

I got an OK from John Welsford for fitting twin rudders to my SCAMP because he also agreed to my use of my existing 4 HP outboard on an inboard motor well. The inboard motor well prohibits the use of a single, centered on the transom, rudder. Could have gone with a single offset rudder but we both seemed to like the twin rudder set up better. I think I have maxed out my question allotment to Mr. Welsford with all my many changes to the SCAMP plans so I am asking the forum for this particular answer.

Here's the two-part question:

If you are replacing a single rudder with two twin rudders, how much smaller than the single rudder can you make each twin rudder? I was thinking about 80% of the single rudder but I'd like to hear from the forum before shaping those little babies. I just finished shaping the offset centerboard for the SCAMP so I know how much work is involved in shaping a NACA foil so I'd like to get them right the first time.

Also in the drawing I commissioned from Mr. Welsford, he has the rudders tilted 5° out from center. Would it be a crime to just keep them parallel to each other in order to make it easier to synchronize the tillers with each other?

Thanks in advance for your answers,
Kenjamin

[Peerie Maa]

80% sounds about right if you do toe them out to 5 deg. I would certainly toe them out as that will make the leeward one more effective when heeled, and also will be more aesthetically pleasing.

[kenjamin]

Thanks Nick,

So if you toe them out, how in the world do you synchronize the tillers since they would be swinging on axis not parallel to each other?

With them parallel to each other, I could have a simple straight bar between the two tillers that could be easily lifted off when needed. I've got no idea how to synchronize two tillers swinging on different axis.

[Bill Huson]

Whatever percentage you use I would make the rudders skinnier to meet to % but make them as long as single rudder. I believe you mean "toe in" as the trailing edges of the rudders are farther from the centerline than the leading edge. This is SOP for catamaran rudders and is called ackerman steering. Rudders on the cat are toed in a couple degrees and the tillers on my cat are curved about 10 degrees toward centerline and connected with a tiller bar. Set up that way the outside rudder in a turn will have a larger turn radius than the inside rudder and effectively the rudders will be running parallel.

If you mean tilting the rudders on the vertical axis you be on your own. I think if that was an advantage single rudder rigs would be tiltable when heeled.

[Hwyl]

You also need to take the Ackerman linkage effect into account http://en.wikipedia.org/wiki/Ackerma...ering_geometry though it's more pronounced on a cat. given the wider separation.

I read about in a book I no longer own, my best guess would be Chris White's book "The Cruising Multihull" (I see it's become expensive) as to linking the tillers a simple universal joint will work.


Edit; Bill wrote much of what I did while I was hunting and pecking

[Peerie Maa]

Here is a starter for 10.
http://www.opensailingusa.com/Boats/.../Features.html

[Hwyl]

This is a nice academic pursuit. Pragmatically I'd go with a centered rudder and an off center outboard on the transom, the same way hundreds of thousands of others do.

[Peerie Maa]

Yo fellow forumites,

I got an OK from John Welsford for fitting twin rudders to my SCAMP because he also agreed to my use of my existing 4 HP outboard on an inboard motor well. The inboard motor well prohibits the use of a single, centered on the transom, rudder. Could have gone with a single offset rudder but we both seemed to like the twin rudder set up better. I think I have maxed out my question allotment to Mr. Welsford with all my many changes to the SCAMP plans so I am asking the forum for this particular answer.

Here's the two-part question:

If you are replacing a single rudder with two twin rudders, how much smaller than the single rudder can you make each twin rudder? I was thinking about 80% of the single rudder but I'd like to hear from the forum before shaping those little babies. I just finished shaping the offset centerboard for the SCAMP so I know how much work is involved in shaping a NACA foil so I'd like to get them right the first time.

Also in the drawing I commissioned from Mr. Welsford, he has the rudders tilted 5° out from center. Would it be a crime to just keep them parallel to each other in order to make it easier to synchronize the tillers with each other?

Thanks in advance for your answers,
Kenjamin

This is a nice academic pursuit. Pragmatically I'd go with a centered rudder and an off center outboard on the transom, the same way hundreds of thousands of others do.

Bit late with that Gareth.

[Hwyl]

Bit late with that Gareth.

Nowt a bit o' poxy won't fix for tha.

[JimConlin]

If the boat will heel much, canting the rudders is a good idea.

As the separation between the rudders is not great, Ackermann geometry is irrelevant.

These gizmos could be helpful in the linkage.

[htom]

Since you're trying for go-fast, you probably have to deal with the drag of the outside rudder in a turn, so an Ackerman linkage like process is going to be added eventually. Same length, maybe 7/8 of the chord. Toed out.

[kenjamin]

Thanks guys, I appreciate the information and the links. I've read in several places where the SCAMP, the boat I'm building, likes to be sailed flat so the idea of one of the rudders lifting out on its own is probably out. More likely if I'm racing another SCAMP, I may try kicking one of the rudders up if conditions are right for that. Those fancy ball joint pieces look expensive but would be fun to play with I imagine. I already own a 4 HP Yamaha four-stroke and it is a bit oversized for the SCAMP so that's why I wanted the motor to be more convenient to use rather than putting it on a bracket on the outside of the transom. Due to a set of unusual circumstances, my SCAMP needs to be a fishing boat, a racer, a micro-cruiser, and a platform for my experimental birdwing rig. Balancing all these duties is probably unrealistic but I'm having fun trying to figure it out as best I can.

Thanks again for the replies, Kenjamin

[JimConlin]

...Those fancy ball joint pieces look expensive but would be fun to play with I imagine. ...

About $9 from McMaster

[Chip-skiff]

I was going to suggest ball joints, but it's a done deal. Not expensive.

If the boat sails best flat, and you intend to follow that practice, one issue might be the increased shear (drag) of the two foils. So you'd want to shape them for the greatest steering effect and the lowest drag.

No doubt you and Welsford thought of this already, but it is worth a mention.

[skaraborgcraft]

I still think one offset rudder is the way to go,but i understand your reasons for doing it this way Ken,even if you are going to increase your drag,and VERY unlikely to ever sail at an angle when one of those rudders will break free. You could make the rudder foils a little shallower in depth,and maybe in chord too,but even 2 rudders @80% of the original size is IMHO larger than needed. Was there any balance area on the foil?.....i dont have my plans to hand. Cheers

[kenjamin]

About $9 from McMaster

Thanks Jim, unfortunately I am so ignorant of what the other needed parts would be that I would have to find more information about how to set up the entire system before I could order anything. I can't help but feel that in race mode my SCAMP would have a lot more to gain by simply kicking one 80% rudder up (when I could get away with it) than by toeing out the rudders.

[kenjamin]

I still think one offset rudder is the way to go,but i understand your reasons for doing it this way Ken,even if you are going to increase your drag,and VERY unlikely to ever sail at an angle when one of those rudders will break free. You could make the rudder foils a little shallower in depth,and maybe in chord too,but even 2 rudders @80% of the original size is IMHO larger than needed. Was there any balance area on the foil?.....i dont have my plans to hand. Cheers

I agree, toeing out the rudders seems like a complicated affair especially since the boat sails flat enough that's it's never going to automatically fly a rudder anyway. As I told Jim, I think there's much more to gain in race mode by simply kicking up one of those 80% rudders whenever I can get away with it. I don't have the plans in front of me either. I'm using the web at my sister's house as is my usual practice but I think there is a little bit of balance area on the foil.

[kenjamin]

I was going to suggest ball joints, but it's a done deal. Not expensive.

If the boat sails best flat, and you intend to follow that practice, one issue might be the increased shear (drag) of the two foils. So you'd want to shape them for the greatest steering effect and the lowest drag.

No doubt you and Welsford thought of this already, but it is worth a mention.

I had to fight pretty hard to use the inboard motor well and the 4 HP with the twin rudders. John told me the 4 HP was overkill but when he realized I already owned it then he went along with my plan for using it in the most convenient way possible (inboard motor well). The 4 HP definitely has advantages for fishing. With my little three gallon remote tank we can fish all over St. Augustine all day long and still have fuel left in the tank. Not many fishing boats can you say that about. And with any luck at all, we can then sail home with fish in the cooler.

[upchurchmr]

Kenjamin,

Ackerman steering does not have toe out as a part of the concept. Set both rudders straight/ parallel to the centerline. If you want Ackerman steering, angle the tillers in to the centerline 2-3 degrees, while the rudders are still straight ahead. This does not address if you want them vertical to the boat at rest or angled outboard at the tip. The bottom/ tip angled out is just so that the rudder on the leeside, with the typical heel angle, will be vertical as heeled.

Ackerman is intended to make turning easier, it does nothing at any other time. It also assumes you are turning around a specific diameter circle so only one turning radius will be the lowest drag. Since your rudders will be close together Jim Conlin is right, this will not make much difference.

I can't imagine any time you would want toe out, I.E., the leading edge of the rudder blades both angled away from the centerline. This will just add drag and typically leads to vibration in cars. Toe in (a little tiny bit) will keep the rudders from oscillating. The best thing about the ball joint rod end shown is that you can screw in one end or the other and adjust the toe in or out as you desire.

At the typical heel angle ?? will you have 100% of the original rudder area in the water calculating the area of both rudders, below the transom?

[kenjamin]

Kenjamin,

Ackerman steering does not have toe out as a part of the concept. Set both rudders straight/ parallel to the centerline. If you want Ackerman steering, angle the tillers in to the centerline 2-3 degrees, while the rudders are still straight ahead. This does not address if you want them vertical to the boat at rest or angled outboard at the tip. The bottom/ tip angled out is just so that the rudder on the leeside, with the typical heel angle, will be vertical as heeled.

Ackerman is intended to make turning easier, it does nothing at any other time. It also assumes you are turning around a specific diameter circle so only one turning radius will be the lowest drag. Since your rudders will be close together Jim Conlin is right, this will not make much difference.

I can't imagine any time you would want toe out, I.E., the leading edge of the rudder blades both angled away from the centerline. This will just add drag and typically leads to vibration in cars. Toe in (a little tiny bit) will keep the rudders from oscillating. The best thing about the ball joint rod end shown is that you can screw in one end or the other and adjust the toe in or out as you desire.

At the typical heel angle ?? will you have 100% of the original rudder area in the water calculating the area of both rudders, below the transom?

At typical heel angle for the SCAMP both 80% rudders will be in the water so 160% of the single rudder but like I said, if I'm racing another SCAMP, I may try kicking up one of the rudders completely (like when sailing downwind) to try to eek out more speed from my SCAMP. When I'm mentioning toe out (evidently incorrectly), I'm referring to the axis of rotation of a rudder being 5° tilted from vertical, not toed in or out as you describe it. In other words, one of the rudders would be vertical if the boat were heeled 5°.

One of the nice attributes of my birdwing rig is that it is pretty well balanced going downwind.

[David G]

Ken,

Did I misread? Didn't you say John drew the new rudder setup? Doesn't he specify what size they should be?

[seo]

Well, I was going to write something based on having sailed E-scows and Hobie 18's, both of which have twin rudders, but then realized that I didn't have any idea what a Scamp was, so found a Youtube of one sailing, and then looked at the plans on Duckworks.
First, as the designer told you, the engine is MUCH too big. I have a 4hp, 4 stroke Yamaha on a 22' O'Day cruising sailboat, and it's plenty of power for a boat that weighs over 2,000 Lbs empty. It's not a light outboard. I also have a 2hp Evinrude 2 stroke that weighs maybe 20 Lbs, which seems more like it. Actually, it looks like it ought to row pretty well...
Second, it looks like she's not going to go faster than maybe 4.5 knots no matter what, simply because she's so short, with so much rocker to the hull.
I wonder if fairly low-aspect rudders wouldn't work out best. I know that at 4 knots the rudders on my Hobie cat don't do much. At 14 kt they are very effective. At low speed, as in coming off a beach, I've taken to leaving the rudders kicked up, so that they are very low-aspect, and they not only steer better at low speed, you can scull with them a little bit too. Same with a Laser.
An E-scow's rudders (and bilge-boards) are splayed out, so that when sailing close to the wind the leeward rudder and bilgeboard is vertical in the water. There's no fancy linkage on the steering, just a cross-bar between the tillers. Same with the Hobie cat. The windward rudder on a Hobie can be kicked up so that you're steering with just the leeward rudder, while the E-scows rudders are fixed. This Youtube shows an E-scow sailing:
http://www.youtube.com/watch?v=_Ex2dFFhpCw
You can see the tiller cross-bar pretty well. The video also shows why it's probably hard to directly extrapolate from an E to a Scamp.
This video shows a Hobie 18 sailing:
http://www.youtube.com/watch?v=Gn8cgQ6sW_o
Right at the beginning you can see a little bit of the rudder arrangement.

[kenjamin]

Ken,

Did I misread? Didn't you say John drew the new rudder setup? Doesn't he specify what size they should be?

The drawing I received from John Welsford addressed several things. He located the birdwing mast on the SCAMP and he drew the bowsprit and two different sized jibs to use with it. He drew the motorwell details although by the time I got the drawing I had already designed and built my own motorwell. There was a problem with my e-mail being too full so I didn't get the drawing in time. The drawing also included suggestions for reinforcing the transom for the twin rudders (5° from vertical) but no information on the size of the rudders. I'm very happy with the drawing but I'm reluctant to bother Mr. Welsford with anymore questions as I've sent him an abundance of information about the birdwing rig that he was asked to consume in addition to all my many changes to the SCAMP plans that he was asked to consider. I'm grateful that he seems curious about the performance of the birdwing rig on the SCAMP and that he was willing to go along with my use of my existing 4 HP four-stroke on an inboard motorwell. I don't really want to bother him with the details about the rudders especially since they are relatively easy to replace (and it gives me something else with which to experiment). He wanted to design barn door rudders for my SCAMP as he considered the fishing to be the biggest priority but I told him I needed the fastest foils I could get my hands on because I would need to be racing other SCAMPs in order to compare the performance of my birdwing rig and speed was very important for that. As I said, I am well pleased with the support he has given me and I just don't want to bother him anymore right now.

[kenjamin]

Well, I was going to write something based on having sailed E-scows and Hobie 18's, both of which have twin rudders, but then realized that I didn't have any idea what a Scamp was, so found a Youtube of one sailing, and then looked at the plans on Duckworks.
First, as the designer told you, the engine is MUCH too big. I have a 4hp, 4 stroke Yamaha on a 22' O'Day cruising sailboat, and it's plenty of power for a boat that weighs over 2,000 Lbs empty. It's not a light outboard. I also have a 2hp Evinrude 2 stroke that weighs maybe 20 Lbs, which seems more like it. Actually, it looks like it ought to row pretty well...
Second, it looks like she's not going to go faster than maybe 4.5 knots no matter what, simply because she's so short, with so much rocker to the hull.
I wonder if fairly low-aspect rudders wouldn't work out best. I know that at 4 knots the rudders on my Hobie cat don't do much. At 14 kt they are very effective. At low speed, as in coming off a beach, I've taken to leaving the rudders kicked up, so that they are very low-aspect, and they not only steer better at low speed, you can scull with them a little bit too. Same with a Laser.
An E-scow's rudders (and bilge-boards) are splayed out, so that when sailing close to the wind the leeward rudder and bilgeboard is vertical in the water. There's no fancy linkage on the steering, just a cross-bar between the tillers. Same with the Hobie cat. The windward rudder on a Hobie can be kicked up so that you're steering with just the leeward rudder, while the E-scows rudders are fixed. This Youtube shows an E-scow sailing:
http://www.youtube.com/watch?v=_Ex2dFFhpCw
You can see the tiller cross-bar pretty well. The video also shows why it's probably hard to directly extrapolate from an E to a Scamp.
This video shows a Hobie 18 sailing:
http://www.youtube.com/watch?v=Gn8cgQ6sW_o
Right at the beginning you can see a little bit of the rudder arrangement.

Yes, I agree the 4 HP is overkill but it is sitting in my carport and it is paid for – plus it has a remote tank which means no refueling at sea, a tremendous range with only a three gallon tank, and a bunch of reserve power should I ever need it. My 4 HP Yamaha is a 2005 model and is lighter than the four horse Yamaha is selling now. Evidently Yamaha is now making their 4 HP from the 6 HP frame as the two now weigh the same while my motor had its own frame size and is lighter. At 47 lbs. my motor is still pretty heavy but will be very easy to attend to on the inboard motor well. I won't have any problem lifting it out and getting it lower in the boat for sailing. I'm fully aware of the maximum hull speed of the SCAMP and I expect to reach that at a little over 1/2 throttle but at that speed the motor could go all day and into the night with very little effort on its part and consume very little fuel.

The other missing bit of information is that the crew size for m SCAMP will never need be more than two because if it's three or more we will simply leave the SCAMP at home and take out Xena, my Caledonia Yawl. So the extra 20 lbs. of weight for the oversized motor on the SCAMP is not a concern as the crew weight will always be light.

John Welsford wanted to design twin barn door rudders for me for fishing but I told him I needed the fastest rudders I could get my hands on because I would no doubt be racing other SCAMPs to see how well my birdwing rig compared to the standard lug sail in the plans and I didn't want to be held back by slower foils. It's kind of wild that I'm needing my SCAMP to play so many different roles (fishing, cruising, racing, experimental rig platform, etc.) but I'm having fun trying to pack it all into one little boat. One thing that's really going for me is that we laid the birdwing mast I'll be using for my SCAMP along Scamp's gunwale and it conforms to it perfectly as if it was made for it (and it wasn't). The mast was a bit under-sized for a SCAMP main mast but I was able to make a mast extension for it that I think will work well and also help with storing the unstepped rig. Due to the size and weight of the components of my SCAMP birdwing rig, I should be able to set and strike the rig on the water. It's very much an experiment but the pieces are coming together nicely as far as I can tell.

Thanks for your comments.

[seo]

You might consider starting out by making a couple of foil-section rudders with an aspect ratio of maybe 2.5:1 (depth:chord). Make them out of mahogany or white pine, a wood that's easy to work and reasonably strong. Just seal them with thinned varnish or S-94 Z-spar sealer, or something quick, and try-em out. It would be an easy matter to make the rudder smaller, until you reached what seemed like an optimum, and then maybe sand it down and sheath it with epoxy/kevlar, or epoxy/carbon fiber if you're feeling flush.
I think that the correct approach to designing underwater appendages is more field experiment than theoretical.
Here's an article about the design process involved in the creation of the Boston Whaler
http://continuouswave.com/whaler/ref...ullDesign.html
Note how much experimentation was involved...

[kenjamin]

I've still got quite a bit of the 18 mm mahogany ply left over that I used for the two halves of my offset centerboard so I'll just use that. I've also got the plans for the single rudder for the SCAMP that I can work from also. I could do something like take 90% of the vertical dimensions and 80% of the horizontal dimensions to yield a shape that would probably work well enough for each rudder. Recently learned how to apply a NACA foil shape to a foil by using a router jig with two rails and then cleaning it up with some grinding and hand pad sanding so I'll repeat the process for the rudders using something close to the foil shape that is provided for in the SCAMP plans.

[Hwyl]

. I've also got the plans for the single rudder for the SCAMP that I can work from also. I could do something like take 90% of the vertical dimensions and 80% of the horizontal dimensions to yield a shape that would probably work well enough for each rudder.

You'll end up with 72% of the area.

Had you considered Michael Storer style Cassete rudders?

[seo]

Maybe 72% of the total area, but that might not tell the whole story. One reason for making the rudder of a beamy boat quite deep is to make sure there's adequate rudder when the boat is sailing heeled over, and the rudder is partially lifted out of the water and operating at an unfavorable angle, square to the angle of heel. With twin rudders, as the boat heels the lee rudder becomes more effective, because it's more deeply immersed and at a more favorable angle, square to force trying to drive the hull sideways.
In my experience, hulls lose it when they roll the rudder up, and the rudder sucks air down and ventilates, or cavitates, or whatever the word is. Twin rudders are less likely to do this, because the lee rudder is doing the work, while the weather rudder is more or less just along for the ride.
This view suggests that twin rudders should be shallower, aiming at the point where when heeled the lee rudder will have the same depth as the single rudder would.
I think that what will turn out is that twin rudders will create more drag than a single, making for a slower boat. If the object is to come up with a racing Scamp, maybe a workable approach would be to have a single "racing" rudder, shipped on the centerline with the motor gone, using oars for aux power when racing. Then for cruising, fishing, towing, minesweeping, etc, ship the twin rudders and re-install the motor...

[kenjamin]

You'll end up with 72% of the area.

Had you considered Michael Storer style Cassete rudders?

Thanks Gareth, now that you mentioned it, I'm reminded how math was not my best subject. But that does sound correct, because we have to multiply the two dimensions to get the area. Thanks for pointing that out.

With the Storer style rudders can you tune in the amount of rudder you want to use by the vertical adjustment? Is there a way to fix it say 3/4 of the way down? I'll check that out. Thanks Gareth

[Hwyl]

Yes, it's a 3 sided daggerboard box, with shockcord holding the dagger style rudder blade in, just slide the blade to the depth you require. you have to think about vertical clearance if you have the mizzen.

[Dan St Gean]

You'll end up with 72% of the area.

Had you considered Michael Storer style Cassete rudders?

+1 Gary Dierking recently used that same setup on his new Va'Motu.



Not only would it be easy to tune how much blade are is in the water, but you could also tune the kick up tension super easily and for that matter unship one rudder for casual use under motor.
Dan

[kenjamin]

Maybe 72% of the total area, but that might not tell the whole story. One reason for making the rudder of a beamy boat quite deep is to make sure there's adequate rudder when the boat is sailing heeled over, and the rudder is partially lifted out of the water and operating at an unfavorable angle, square to the angle of heel. With twin rudders, as the boat heels the lee rudder becomes more effective, because it's more deeply immersed and at a more favorable angle, square to force trying to drive the hull sideways.
In my experience, hulls lose it when they roll the rudder up, and the rudder sucks air down and ventilates, or cavitates, or whatever the word is. Twin rudders are less likely to do this, because the lee rudder is doing the work, while the weather rudder is more or less just along for the ride.
This view suggests that twin rudders should be shallower, aiming at the point where when heeled the lee rudder will have the same depth as the single rudder would.
I think that what will turn out is that twin rudders will create more drag than a single, making for a slower boat. If the object is to come up with a racing Scamp, maybe a workable approach would be to have a single "racing" rudder, shipped on the centerline with the motor gone, using oars for aux power when racing. Then for cruising, fishing, towing, minesweeping, etc, ship the twin rudders and re-install the motor...

Actually it was James McMullen that suggested I leave the motor home if I get the boat done in time to take to the Mystic WoodenBoat Show at the end of June. And the more I thought about that, the more it made good sense. First of all, sure don't need no stinking motor to navigate that little pond of water they have in the estuary up there. Secondly, any fool can build a motor mount and it might distract somewhat from my birdwing mast to have that big ole motor there on such a little boat. With the motor pulled I entertained the thought of building a "quickie" rudder that I could mount on the engine mount and I could just leave the rudder hardware there as I found that the motor would mount around the gudgeons with no problem.

So yeah, I could mount a single rudder for racing and yeah isn't it kind of wacko to be so concerned with racing a 4.5 knot capable boat? Such is my life. Thanks for the suggestion, Seo, it's a good one. The minesweeping duty is something I hadn't thought of but towing my sister's boat is definitely a possibility. Thanks again for your input – seriously!

[kenjamin]

+1 Gary Dierking recently used that same setup on his new Va'Motu.



Not only would it be easy to tune how much blade are is in the water, but you could also tune the kick up tension super easily and for that matter unship one rudder for casual use under motor.
Dan

Thanks Dan, I kinda had an idea of how it worked but the picture certainly spells it out. Does that little unfinished looking strip of vertical wood go to the aft of the white part when the rudder is fully down? Or is it there to stop the downward progression of the rudder? Thanks again, kenjamin

[Dan St Gean]

I can't be sure but it looks like it slides just aft of the casette rather than being used as a stop. Gary also mentioned the kick up feature works both ways which is nice if you get pushed back up the beach by a wake or a wave.

[kenjamin]

I can't be sure but it looks like it slides just aft of the casette rather than being used as a stop. Gary also mentioned the kick up feature works both ways which is nice if you get pushed back up the beach by a wake or a wave.

Very cool! Thanks Dan.

[Dan St Gean]

Another nifty bit is you can pull them up for really shallow water sailing without the hard steering that kicked up blades produce. It will also be instructive on just how much rudder your boat needs for given conditions simply by sliding it up and down a bit at a time.

[kenjamin]

Hey Dan,

I've been experimenting with pex pipe (polyethylene tubing) as wear surfaces for applications where normally there would be wood rubbing on wood. So far I'm using it in my bowsprit channel and on the bowsprit itself so the darn thing doesn't get stuck. I'm also using it in the mast extension for my birdwing mast for the SCAMP for the same reason. I can't help but wonder if the sliding cartridge for the rudders wouldn't be another place to have the smoother action the pipe provides. I realize you need a certain amount of friction to get the rudders to hold their position but the plastic sure makes everything work smoother and provides a wear surface that doesn't shed paint. Here's some pictures.

This is the mast extension before I closed it in with four more side panels.





Here's the pipe in the bowsprit channel. The bowsprit will have two pipes on its underside and two more on its sides.



The pipe was opened up on the table saw and then forced open wider to fit around wood. Still perfecting the technique.

[Phil Y]

I'd have said somewhat less than 80%. My boat (50' ketch) has twin keels and twin rudders. The pics aen't great but might give you a general idea-you'll see the rudders are toed out. And are pretty tiny for a 50' boat. (The skegs are quite a bit bigger than the rudders.)

[skaraborgcraft]

Looking good Ken,nice job fairing that board. Like the poly-pipe idea,tough stuff. Cheers

[kenjamin]

I'd have said somewhat less than 80%. My boat (50' ketch) has twin keels and twin rudders. The pics aen't great but might give you a general idea-you'll see the rudders are toed out. And are pretty tiny for a 50' boat. (The skegs are quite a bit bigger than the rudders.)

Thanks Phil,

Keep in mind that the SCAMP I'm building is only 11' 11" long so don't know how much carries over to my little boat but I appreciate the pictures. That's a lot of boat you got there, bud.

Thanks again for the pics, Kenjamin

[kenjamin]

Looking good Ken,nice job fairing that board. Like the poly-pipe idea,tough stuff. Cheers

The stuff's about as slippery as chopping block plastic folks use for chopping up the vegetables but the really good news is that it's cheap and extremely light. I keep meaning to write a letter to some of the manufacturers of it to see if they would be interested in making a sunlight resistant version of it for outdoor applications such as mine although so far most of what I've done with it won't see much sunlight. Seems like they would just have to add graphite to limit light penetration and might also add to its slipperiness. Thanks for the encouragement!

[xsboats]

How do you plan on attaching the 2 Piver amas to your Scamp?

[kenjamin]

I was figuring on having the the cross-beams low enough to the water to where I could just power the SCAMP up onto them with my big bad 4 HP Yamaha. Ya know, kinda like those boats designed to accept jet-skis.

[Tom Robb]

Everyone seems to be takeing this twin rudder thing seriously so perhaps I may be missing something, but what purpose do twin rudders serve on a Scamp when she's supposed to be sailed flat which would keep a single rudder immersed?
Just wondering.

[kenjamin]

Everyone seems to be takeing this twin rudder thing seriously so perhaps I may be missing something, but what purpose do twin rudders serve on a Scamp when she's supposed to be sailed flat which would keep a single rudder immersed?
Just wondering.

Here's the full story of how I ended up with twin rudders. It was mostly because I had an existing 4 HP motor that I wanted to use on my SCAMP but didn't want to have to hang over the transom to tend to it.

http://forum.woodenboat.com/showthre...birdwing-SCAMP

[Tom Robb]

So, it all flows from the, probably not so good, idea of keeping the 4hp motor?
Your boat, your choice.
I'd skip the motor and build Scamp as designed. You, obviously, are of a different mind.
So be it.

[Dan St Gean]

Tom,

You might have missed that Kenjamin is going to motor out, fish (most likely under motor) all day, step the mast, and sail back. On his tidal canal, sailing to fish wouldn't really work. He's got a post somewhere explaining his circumstances.

[kenjamin]

So, it all flows from the, probably not so good, idea of keeping the 4hp motor?
Your boat, your choice.
I'd skip the motor and build Scamp as designed. You, obviously, are of a different mind.
So be it.

Hey Tom,

Another bit of information regarding my situation is that the 4 HP also occasionally powers my Caledonia Yawl, Xena. So it has to do double duty. Yeah, the 4 HP is overkill for the SCAMP but it does have several advantages besides being already paid for. It has a remote tank so no refueling at sea is required. The remote tank gives it incredible range and in fishing mode we do a lot of moving around motoring up salt water creeks and trying different spots throughout the day. The type of fishing my cousin and I do requires a motor and simply couldn't be accomplished under sail alone. Another advantage of the 4 HP is that it doesn't have to work very hard to move the SCAMP. The SCAMP will reach hull speed at about half throttle and the 4 HP is very quiet at that speed and, like I said, can run all day long and into the night with just a three gallon remote tank. Thirdly, if conditions get bad, the 4 HP has plenty of reserve power to fight adverse currents in the Matanzas River, steam against contrary winds, or tow my sister's boat, a little Skerry, when I get that call from her. Notice I didn't say "if", I said "when" I get that call.

John Welsford was reluctant about me using the 4 HP on the SCAMP but when he realized I already owned the motor he agreed to the inboard motor mount and the twin rudders. The inboard motor mount will make it much easier to pull the motor out and then get it lower in the boat for sailing. The motor makes it possible to do the kind of fishing we like to do. The motor mount makes it possible to easily stow the motor and then sail home. This is a good plan for me as you can plainly see:

[kenjamin]

Tom,

You might have missed that Kenjamin is going to motor out, fish (most likely under motor) all day, step the mast, and sail back. On his tidal canal, sailing to fish wouldn't really work. He's got a post somewhere explaining his circumstances.

Thanks Dan, for trying to explain my fishy tendencies. My tidal canal is actually the Matanzas River and the best fishing grounds for the redfish we like is about 4 miles away from the boat ramp around the corner from my house. There's also the option of trailering across town to a closer ramp so that we'd only have a mile or so to motor with the 4 HP. The bait shop for the live mud minnows that the reds like is right on the way to the further boat ramp so that is what we will do most times. I bought minnow traps and a pin fish trap so maybe someday I'll get it together enough to catch my own live bait.

Even though the 4 HP is a bit over-sized for the SCAMP, it is way under-sized compared to what most everybody else fishes with for the same fish we will be harvesting. I don't feel bad at all about the little bit of fuel the 4 HP uses. Tom thinks my use of the 4 HP Yamaha is a bad idea only because he's never tasted my baked redfish!

[James McMullen]

I think your carefully shaped new CB foil is looking great, Comrade! That's a nice start indeed. After you're done with Scamp here, I think you should keep those techniques in mind and give her big sister Xena something for X-mas for herself this year. She'll love it, I promise.