Repair of *lumpy* bottom from trailer damage

[K.C. Walker]

Bob,

Mike sent me this picture a while ago and it gives a little view of the "post". I think he might've sent me a better one but I can't find it.

[Mike Gillum]

Bob,
The hull of #2772 BUBBA (Butt Ugly Blue Boat Ahead) is still factory original and several different shades of Blue courtesy of the previous owners hence the name.
Hiking hard while going upwind in the windiest race at last year's DS NACR's on Galveston Bay in Seabrook, Texas in 2-3' chop and 18-22 knots I can still clearly see the chop roll down the inside of the bottom under BUBBA from the bow towards us as the rolled edge of the windward seat repeatedly pinched the backside of my legs as the top of each chop passed underneath us.
"Flexible Flyer" came to mind more than once but we won the race going away and I was told years ago never ever to mess with fast!
Other than replacing the trailer and updating the Spars and Foils the single biggest improvement to BUBBA was structurally tying the Cuddy Cabin to the front of the Centerboard Trunk using a pair of radiused .120 x 1 x 2" rectangular aluminum Tubes to form a "Tree" shaped to a curved "H" that has a 24"+/- long curved 1/4 x 2" aluminum Flat Bar rolled to match the bottom of the Cuddy and thru-bolted to the Cuddy Cabin as well as being thru-bolted to the top front edge of the Centerboard Trunk to hold the hull and deck in a horizontal plane.
In between the top and bottom connections to the Cuddy and Trunk are three horizontal welded pieces of 1/4 x 2" aluminum Flat Bar that create "trays" for cleats for the Cunningham & 3:1 Jib Halyard Fine Tune (top), Main Halyard (middle) and Jib Halyard (bottom).
K.C.'s photograph of BUBBA from astern shows part of the "Tree".

[Bob Perkins]

Mike - thanks for the info!
We have been contemplating vertical and cross bracing for the race boat and have seen a few different designs. Proven is always a good one to seriously consider!
The other one we have been toying with is vang control for the driver somehow w/o creating a rope factory..
Great help everyone.
Thanks

[GreenLake]

I've taken the liberty of moving the discussion of the boom vang to the Rigging forum, where it might be seen by more people interested in that subject.

[K.C. Walker]

I got a nice note from Mike including some photos of variations on the “tree” to stiffen up the boat. Below is quoting from Mike’s note and some photos. Thanks Mike!

“I pulled four photographs of #307, #316, #2772 & #11026 showing the different methods of tying together the boats structurally.
Dave restored #11026 three years ago and rather than spending the money to fabricate an aluminum “Tree” choose to laminate one out of wood instead.
Since then Dave has restored #1076 that he raced at 2011 DS NACR’s, retired from the State of California last year, restored #2365 that he raced at 2012 DS NACR’s and is currently rebuilding a McLaughlin that Michael & Brook Measures bought from the Skeens last year.”

Steve Lowry #307


Mike Gillum #2772


Dave Keran #316


Dave Keran #11026

[Bob Perkins]

I like both of those tree designs!

I could pretty easily make the wood version.
The aluminum one I would have to have made. I can see how they both provide the bracing needed for the shrouds.
Thanks for the great info!

[jeadstx]

I don't have a DS1, but I'm restoring a Rhodes 19 and those tree designs look like something that might work for me on the Rhodes 19. The open cuddy cabin is similar to the DS1 and extra support for the cuddy cabin roof plus additional places to run lines looks like a great idea.

John

[GreenLake]

Interesting. In the photos only Dave Keran's #316 appears to have the full forward bulkhead. None of the trees would seem to give the same stiffness against lateral movement of the deck as is provided by having a bulkhead. The wide wooden tree for #11026 has a small diagonal component (as does Mike's). I wonder whether that's truly enough to compensate. (Of course, bracketing the CB trunk the way they do adds additional resistance to sideways motion - some of the twisting forces will be transferred via the CB trunk to the thwarts.)

[Bob Perkins]

Both Trees make perfect sense to me on stopping wracking/compression of the sides by the shrouds
- The tree is attached to the top and bottom of the centerboard trunk - which is very important!
- The top of the trees are attached to the cabin top and are wider to spread the load. The curvature adds stiffness as does the cross pieces.
This alone does two things
- The cabin top can't rise up due to shroud tightening (and also can't compress from standing on it)
- If the rig pulls on one side of the boat (think upwind) - any wracking of the front of the cabin will push the top of the tree sideways.
That will get transmitted down to the centerboard and move the boat. No wasted energy squishing the hull.
It appears in both cases that the trees are in the same plane (or pretty close) to the shroud attachment points which also eliminates the ability for twist.

It looks like the wooden tree only attaches to the cabin face - while the metal one has a strap that attaches directly to the cabin top at multiple spots.
In both cases - I bet the design locks up the geometry of the wide part of the boat nicely - transmitting any distorting forces to the centerboard and making the boat move as opposed to just changing shape.

[Mike Gillum]

Greenlake,
Steve Lowry's #307 and Dave Keran's former #316 (Craig Lee now owns #316) are both restored and updated "Three Digit Classics" with the bow tank being full height from the foredeck to the keelson rather than the later four & five digit DS with their shorter bow tank present in #2772 & #11026.
Both #2772 & #11026 have the required compression struts per DS Class Measurer requirements between the underside of the foredeck and top aft edge of the bow tank replacing the cosmetic bulkhead with it's removable doors.
Dave Keran did add an additional compression strut to #11026 just forward of the mast and everytime I'm either installing or removing the mast from #2772 and feel the Cuddy Cabin deflect under my weight in front of the hole for the mast I think I should also do the same thing but never remember to after I'm done standing on the Cuddy Cabin!
For racing purposes the cosmetic bulkhead with it's removable doors only add weight without serving any function so out they went!
One of the many hats I get to wear at work on a fairly regular basis is "Structural Engineer" though I have neither an P.E. or S.E. after my name!
Easiest way to think about the compression created both by the rig under load at the dock and underway is to take a red Solo Cup by the top lip and if you squeeze it at opposite sides at 9:00 & 3:00 O'Clock you'll quickly bend it out of a circle into an oval but if you hold the other two opposite sides at 12:00 & 6:00 O'Clock in a fixed location the same amount of pressure at 9:00 & 3:00 O'Clock will not produce the same oval without considerably more pressure.
The "Tree" achieves the same thing by holding the top of the Cuddy Cabin to a fixed distance from the centerboard trunk even after the forestay is at 300# according to my trusty Loos Gauge.
I originally intended to through-bolt the base of the "Tree" on #2772 but found that location to below the waterline which created a significant leak and I quickly pulled the SS Bolt and applied Duct Tape to cover the holes on both sides of the trunk leaving only the top SS Bolt to attach the "Tree" to the trunk. I've never seen any form of movement between the bottom of the "Tree" and the trunk so I've never gotten around sleeving a larger hole with fiberglass rod to make it waterproof and through-bolting it.
I'm sure there's a slight decrease in overall distance between the chainplates before attaching the shrouds and after loading the rig but its neglible to the overall performance in comparison to a bad start, poor sail trim, missing the first shift,..........?
Originally #2772 came with a square stained mahogany "Tree" in the same general location as the present aluminum "Tree" along with a small brown Snubbing Winch on the aft side of the "Tree" for trimming the Jib Sheet and after removing the Snubbing Winch a revelation came to me that a new updated "Tree" would be an excellent place to be able to locate the Main & Jib Halyard Cleats as well as Cunningham & 3:1 Jib Halyard Fine Tune Cleats while sturcturally stiffening the #2772. Win/Win!

[Bob Perkins]

Nice Description

Glad to see I was thinking in the right direction.
I may have drilled leaky bottom holes - now I'll watch for that

[GreenLake]

And I second that, a really nice description, Mike, especially the Solo cup example.

I would not underrate the effectiveness of the "cosmetic" bulkhead in resisting the kinds of stresses that we are talking about - except, it's main drawback is that it's not located in the same plane where these stresses are generated. The trees have a considerable advantage in that regard. A frame-like design might have additional strength when loaded asymmetrically, but especially with the wide trees (instead of just a post) there's probably enough strength there for the purpose.

Btw, I've not observed any alarming amount of flexing on the cuddy roof when walking on it - the foredeck is another matter. But then, I raise my mast from the cockpit.

Finally, I don't quite follow your discourse on chainplate distance. If I follow your example, the tree would be loaded in tension as the rig would push the keel down and the chainplates up and closer to each other (making the cuddy open up). Seems to me, you could control the final distance with the length of the tree..

How does chainplate distance affect the sailing trim?

[jw]

With respect to installing a "tree" or any other vertical stiffener, how did you handle mounting it to the upper part of the cuddy? As I recall there is a deck stiffener that runs close to the back edge of the cuddy.

Great thread BTW!

[Mike Gillum]

jw,
The "Tree" on #2772 has a piece of 1/4 x 2" aluminum Flat Bar welded to the top of the curved 1/8 x 1 x 2" vertical members of the "Tree" that was rolled the easy way to closely match the underside of the Cuddy Cabin though that isn't as nearly smooth and even as the top of the Cuddy Cabin.
It's through-bolted just in front of the rebar reinforcement in three places (both ends & center). The rolled Flat Bar is approximately 20" long helping to spread the load it carries over about half of the aft edge of the Cuddy Cabin.
Zero movement either vertically or horizontally when I step up on it.

Greenlake,
Pretty sure (not 100% but close to it) that the windward chainplate isn't affecting overall sail trim or performance as I don't see any movement in things like the Jib Sheet or Barber Hauler Block rising or falling relative to the aft top edge of the Cuddy Cabin where I would easily pick-up any movement if the windward chainplate was moving effectively "whipping" the Mast.
Keep in mind that the only chainplate under load going upwind is the windward one as the leeward shroud is usually loose and rolling around even under the high rig loads we run as the DS Mast will be bowed both towards the bow and to windward under most circumstances decreasing the true distance between the hounds and leeward chainplate thereby creating the loose leeward shroud.
Some people may think that the chainplates are being pulled upward creating the loose leeward shroud though I would suspect that the forestay stem fitting has a far greater chance of being pulled upward vertically because of the greater distance (re: lever arm) between the bow and Mast versus the chainplate and Mast.
100% sure that I don't want to know just how much #2772 is bending!

[GreenLake]

Greenlake,
Pretty sure (not 100% but close to it) that the windward chainplate isn't affecting overall sail trim or performance as I don't see any movement in things like the Jib Sheet or Barber Hauler Block rising or falling relative to the aft top edge of the Cuddy Cabin where I would easily pick-up any movement if the windward chainplate was moving effectively "whipping" the Mast.
Keep in mind that the only chainplate under load going upwind is the windward one as the leeward shroud is usually loose and rolling around even under the high rig loads we run as the DS Mast will be bowed both towards the bow and to windward under most circumstances decreasing the true distance between the hounds and leeward chainplate thereby creating the loose leeward shroud.
Some people may think that the chainplates are being pulled upward creating the loose leeward shroud though I would suspect that the forestay stem fitting has a far greater chance of being pulled upward vertically because of the greater distance (re: lever arm) between the bow and Mast versus the chainplate and Mast.
100% sure that I don't want to know just how much #2772 is bending!

OK, let's see whether I can put this into my own words in a coherent way. That's the best test I know to make sure I've reached the same understanding.

Under sail, upwind, the sails impart a force to leeward on both mast and forestay (and the stemhead fitting, but I think we can ignore at least the leward component of that contribution). There are also leeward forces on the sheets, but we don't worry about them, either. So, the mast is pulled downwind, the sideways pull on the forestay increases its tension, pulling the mast forward (while the mainsail, as well as the swept-back shrouds will pull a bit backwards). Resisting this downing pull is the upwind shroud, which elongates a little, allowing the mast to give, which de-tensions the leeward shroud (and fore-stay).

If the hull near the cuddy opening acts like your solo cup, the chainplate comes a bit in (and a bit up). For the same tension on the upwind shroud, the mast would give a bit more, because the effect of the moving chainplate is the same as more elongation on the shroud. Essentially, the shroud acts like it's softer. If the boat heels, the buoyancy would concentrate under the downwind chainplate and the boat would deform on that side as well, if it's sailed flat, there's a more asymmetric deformation on the hull. Do I have that right so far?

As you mention, the forestay should be pulled up a bit as well, but I think lever arm alone is not a good consideration in predicting the magnitude of the effect. In the forward area you have the full-strength hull-laminate form a step V, which puts that laminate at nearly parallel to the plane in which the bow would have to bend. The equivalent example to your Solo cup would be the business card, folded length wise into a V and stapled on one end. That structure resists bending very effectively - any bending would be concentrated in an area near the "open" end. The foredeck being flat also may be stronger on compression than the curved cuddy-opening. For all these reasons, I would expect the hull to be naturally much "stiffer" in that direction (at least up to the mast step).

Now your stiffening the center of the cuddy has the effect of making the upwind shrouds stiffer, by maintaining the location of the chainplate. Because the shrouds are swept back, the upwind shroud counteracts the forestay pull better when it's stiffer, so mast-bend at the shroud attachment point should become less (and forestay sag should be less).

All things being equal, the forces on the shroud and forestay should be nearly the same as before, because their overall magnitude and direction is governed by the aerodynamic effect of wind on sails. Any change would have to come from better aerodynamic efficiency (effectively better trim) available with less forestay sag and different mast bend.

Is that about the size of it?

Now for the jib, I can get my head around that it might work more efficiently with less forestay sag. But how does the main benefit?