Rake and Tension for E-38

I am finishing up my hydralic BS adjuster install and I think I am going to be shortening my headstay a little as well, as I was never able to get the forestay sag the way I wanted without what I felt was too much rake. I would love to hear what other 38 owners are using for a base rake setting. Say for 8-10kts. Obviously less than 8kts probably more headstay sag and less rake, over 10 more rake and less sag. I would love to hear either measurements from the masthead to the transom or maybe degrees, or even "when I hang a hammer or heavy weight from the main halyard it sits 8" back from the mast at the gooseneck"... Since I am going to be cutting my backstay to install the hydralic unit I would like to get the rake set so that I will have a full range of adjustment from light air to honking. This rig is fairly flexible as well so I know I will get some prebend with the hydraulic adjuster at different settings so any comments on ideal prebend settings would help too. I know these settings are going to be dictated primarily by the cut of the main too. Attached are some shots of the modified stern pulpit. My buddy was real nice with the stainless welding, hardly had to do any buffing to the welds. But then he works for a local fab shop and does this stuff all day.

Hi Ted,

Unless I read your questions incorrectly, there might be some confusion about the terms "Rake and "Prebend". Just in case that is true, I will try and clear it up..

1). Rake-I, like you, would love to know what a baseline rake setting is for the 38. We have these dimensions for boats like the Ben. 36.7 and 40.7, Melges 24 and J 24, etc. But I doubt anyone recently has raced a 38 seriously enough to sort that out exactly. This is usually defined in terms of a HS length-done using the jib halyard. Being One Design boats, many have a max limit on HS length, and in other than very heavy air venues, this is what it is normally set to. My guess for the 38 would be about 1" of aft rake, at most-because she is tippy and powerful to begin with.
The reason we go max length is to get the MOST rake, with ADDS weather helm-making the boat point higher (which is key in buoy racing). We offset this weather helm issue with max crew weight and aggressive sail trimming.

For general purpose cruising, any of these boats will want LESS rake-to have a more neutral helm in most conditions.

Rake aft moves the center of effort AFT of the CG, which INCREASES helm and pointning in light air, but on a cruiser may result in excessive helm pressure. Rake forward does the reverse. I say this to make the point that you made the comment of more rake in higher winds, less in lighter air, and the truth is exactly the opposite. In your Chesapeake summer days, ideally you want max aft rake in the light air, and less in heavy air. If you were going to actually make those changes, you would do it by adjusting the HEADSTAY-not the backstay. Longer HS in light air and shorter in heavy air. The reality is most boats pick a setting, and simply use the backstay to control BEND (but not PREBEND or RAKE). The backstay does not affect RAKE.

2).Prebend is the bend set into the mast by a combination of the mast step, deck partners, and fwd and aft lowers. It is NOT affected by backstay-it is called prebend because this is the bend in the rig BEFORE any backstay adjustment is made.. For the 38 (masthead rig, in line shrounds), assuming a centered step and deck partner (to keep this simple), to induce more prebend, you would load up the fwd lowers relative to the aft lowers (with zero load on the backstay). This will induce some bend in the lower part
of the mast. The main reason for doing this is to match up the mast with the mainsail-or as in some fractional boats (which use different shroud tensions to do the same thing)the rig needs a certain prebend to be stable, and the main must be cut to match this.

Either way-the backstay produces BEND, but not RAKE or PREBEND..

Let me know if if this is clear-contact me directly if you wish, and good luck!!

S

When I replaced my RF I added about 2 inches to my HS wire. I wanted to see the effect of going upwind with a more raked mast. I figure I could always adjust the turnbuckle down to remove the rake or worst case, easily shorten it again since its a mechanical fitting. I guessed my upwind performance may be a little better with more WHelm otherwise being the trade off.

Boat does go upwind nicely and with the new sail, WH isnt an issue. Still waiting for the new full size main to see how that works.

I dont have a measurement but I will try the plumbob method and see what I get. Only issue I can see is that my trim changes depending on the water/fuel tanks.
The bow will drop 2 inches when the fwd tank is full. And the level in the aft fuel tank makes a difference too. Since I didnt put the original waterline on the boat I dont know where the "lines" should be. Maybe a stem to waterline measure would help?
I'm curious too to get a reference measurement.....(maybe I just want that cool J-boat look. )

It's all good!

Ben,

Right you are-and I'm sure that when you are in performance mode, you will notice more helm and a slower boat with that fwd tank full. Your observations are dead on!

I realize that my more performance oriented point of view is not of universal interest here, I do think it would be awesome to have the result of this thread be a real tuning guide and quantitative data collection for the 38.

Looking back, this boat is a surprisingly competitive boat at club level racing, and for those who are in that mode (Ben, Ted, etc.), we are on track towards establishing key factors to maximize performance. The standard things apply no matter what: MINIMUM on board gear, and MIN fluids in the tanks, MAX crew, clean bottom, decent sails..That is the starting point for any boat, and here we can zero in on deck gear, rig tuning, and technique!

For those who think I might be a sailing :nerd: , you might be right!!!!

Cheers,
S

I'm with you Seth. My thoughts on rake were that as I add pressure to the adjuster to control headstay sag I am likely to add rake at the same time. Typically add more tension in heavier air so I am thinking I will end up with more rake then. Probably will end up with more bend (sorry to say prebend when I meant bend) with more tension which should be better for flattening the main. When you say 1" of rake, how are you measuring that? With the plumbob off the main halyard? In terms of measuring headstay length for rake I am bringing my tuning thoughts from my one design dinghy (www.jet14.com). We measure rake from masthead to transom distance, then tension on the side shrouds. Prebend by pulling the mainhalyard to the gooseneck and measuring the max deflection of the mast, at the dock not while sailing. Thoughts.

Gotcha

I figured-this is a common conception.

Generally we don't associate rake with backstay adjustments-just bend. What really happens when you add backstay is that the mast will bend aft, which will flatten the main-which is what you need as the wind pipes up.

When I said about 1"-yes from a plumbob on the main halyard.

Check out any of the J boat guides (J 35, J 30 J 24) to see how rake is determined on the bigger boats...

Whwn I have a minute I will try and paste one of those....
cheers,
S

Tuning

Check out this little excerpt from the Ben 36.7 tuning guide-note the description of the HS length and what it is for. For the 38, I am guessing most parts of the J35 tuning guide (Google J35 tuning guide) will be very useful. The 36.7 guide can't really be used for the 38 because it is a frac rig with swept spreaders-so the whole process is quite different. The J 35, which is masthead/inline spreaders, will be pretty close.

Base Rig Set-Up
Mast Butt – Proper mast butt location is the critical first step in setting up the rig to achieve proper boat balance and mast pre-bend. The mast butt should be positioned so the forward edge of the mast is 26cm from the bulkhead. This should be one hole aft of max forward on the step, but you should check the bulkhead measurement to be sure. You may need to modify the floorboards that sit around the mast slightly in order to allow for this position.
Headstay Length – The headstay length will set the base rake of the boat. The base headstay length, measured using the centerline halyard to the bow of the boat at the sheer should be 14.48m (47.5’). This is a good all-purpose headstay length.
Center the Rig - Put a mark on the rail of the boat on one side even with the chainplates. Measure this distance from the headstay attachment on the bow. Put a corresponding mark on the other side, the same distance from the headstay. At this point the Upper Shrouds (Caps) should be hand tight and the Intermediates (D2s) and the Lowers (D1s)

Enjoy!
S

Googling and will be reading... Thanks Seth. Okay I read the guide. Sounds like they want the butt max forward and the mast collar(?) max aft to develop 1.5" of prebend. On the prebend do they measure that by mainhalyard pulled taught to the gooseneck? That does not sound like much bend to me, but that is for a base setting. Are they inducing bend from the mast collar? I have a rubber wedge thats in there until I pull the spar next, but I would consider moving my butt. I guess I will see what rake I have now. Try to get to the 1" Seth mentioned and go from there. I am going to be shortening the backstay to add hydralics and want to have a good spot to shorten from.

Guess this is another topic but Ben what are you using for headsails? Furler? 150%?

Now we're talking!

Ted,


OK-keep in mid these are settings for the J boat. Since nobody cares if your J measurement is spot on (under IMS/IRC the J can change as you move the mast in the partners-all the way forward and your J gets a bit smaller-as will your headsails since the LP is a function of J-and your rating)-For now, leave it where it is, and I would leave the step alone, too, until you see the new main. Yes, use the main halyard as you describe (plumbob for rake, main halyard for bend). Do NOT even mess with the fwd and aft lowers until you see the new main-unless you know how much luff curve they are putting in.

My advice is the set the rake at about an inch-then measure the headstay and note this value (we'll come back to this later).

Go sailing with the new main. With a loose backstay and the lowers as you have had them (assuming you liked the way the mast behaved), the main should be quite full. Then go to about 80% of max backstay. If all is set up correctly, the main should be BOARD FLAT-even a wrinkle going from the clew to the mast is OK (called an inversion wrikle because the sail is "inside out"). If you can't get the sail this flat at 80% of max backstay, start by adding prebend by easing the aft lowers about 1.5" and taking up on the fwd lowers the same amount-see what happens. If still not enough do it again until you have induced about 1.5 " of prebend. If that won't get you flat with the 80% BS, the next step is to move the mast AFT in the step. If after doing all this you still cannot get the main board flat, the main may simply be too full (I would guess you are seeing about 8-9" total bend at this max setting). If they have used more than 8-10" of luff curve you may have trouble getting it flat enough and need a recut.... BUT...I highly doubt they will use more than 5-6" (what I would use as long as I have a hyd adjuster).

So, while those are the steps, I doubt you will need to go very far in the process.

Apart from all of this, there IS an element in the rake equation where the fwd most step setting will help incude more aft rake, and the aft most will do the opposite. I have not mentioned this becasue most of the 38 types (a normal cruiser racer mentality) will not be as consumed with rake, and simply using a HS length is plenty sophisticated for club racing!

Once you have that magic HS length for the base setting (lets play with the 1" number for now), it is simple matter of increasing the HS length if you find you have too neutral a helm in light-moderate air and/or are not happy with your pointing. Keep dropping it back until you get the right combination of performance and feel (you should take up or let off an equal amount on the little turnbuckle that comes with the Hyd backstay adjuster when you make the HS adjustments so that the adjuster still has the same effect on HS sag). All you are doing is moving the top of the mast fwd or aft-which is changing......tada: RAKE!!!! And if you do as I suggest, you will still get the same amount of bend with the backstay-regardless of what amount of RAKE you are carrying. If you want to really get optimal, establish HS lengths for 0-5, 6-12, and 12+ knots of wind. Write them down, and "season to taste" on race day-it will help.

When going downhill, be sure and let the BS ALL the way off (to get rid of as much aft rake (and hence weather helm) as you can. When I said in a previous post BS does not affect rake-I meant in the sense of upwind/reaching/controlling mainsail shape. If you let it all the way off while going downwind, the tip will of course go fwd. You might also take the Genny halyard down to the jib tack fitting and grind it snug to get the slack out of the backstay (and put lots of slack in the HS). This will get the mast as far fwd as you can-noticeably faster when going downhill. This is a big advantage of in-line spreader boats as opposed to swept aft types like the 36.7, J 30, etc. because on those boats the upper shrouds control the HS tension to a large degree, and you can't easily back those off when going downhill in a buoy race!! In-line spreader boats, frac or masthead, can have the top of the mast move as needed to add or reduce helm.

In case this part was not clear, a fwd raked mast helps dowwind speed as much as an aft rake helps upwind speed-the idea is to give the boat a bit of "help" (a little weather helm will point higher, and a little lee helm helps you dig deeper).

We are getting pretty deep in the performance angle, but it is good stuff!!

Let me know how the main fits!

Seth

Thanks for that Seth, All great stuff. Now if it will stop raining I could play....
I'll let you know how the max roach main works out.

Ted, I have a 135 and a 100 with a high cut clew. Its usually blowing 25 to 30 in the slot here so i keep the 100 on most of the time. I have a harken 1.5 RF. I'm thinking Im going to need a 150 for down in SanDiego (mostly like summer Ches bay conditions)

No worries

Glad you are enjoying the thread-it is fun to review all of this from my perspective as well...

Did I get it confused about who was getting the new main? Sorry if that is the case...I thought perhaps Ted was because of the specifics about prebend and rake-but maybe that is to match up with a recent or current mansail-sorry if I got that backwards, guys-hopefully you get the point:
I'm looking forward to hearing how all of your various tuning exploits work out, whether it is Ben, Ted, or any of the great folks on the site!!

Cheers!!
S

Yeah no worries Seth. I got my new main last summer. I am going to get a new headsail this year but probably not till fall. I am thinking I will get more bang if I try to get a good AP assym for racing and try and get by with my headsails till fall discounts come up. Regarding the J-35 tuning guide. They discuss butt location and mast collar location, along with forstay length. They mention trying to achieve 1.5" of prebend, but they dont give a rake number per say. They dont say "At a forstay length of ... you should have ... inches of rake" I am going to start with the 1" Seth mentioned and probably tune to 1.5" or so of prebend and see what my main looks like. May need more or less prebend to get it looking right. Will keep you posted.

Ben on those headsails are the 100 and 135 furling? If so what do you use for a furler?

Gotcha

Cool! Also, you have the right idea on the AP A-sail-especially if your headsails are in reasonable shape.

On the J 35 guide-that is precisely my point: It is not really important to know exactly what the rake # is as long as you have a headstay length number, since this is a much more precise and repeatable dimension.

So, set that 1.0-1.5" of rake, measure the HS length, and then forget about rake per se. Just lengthen or shorten the HS as needed until you get what you need.

Again, keep in mind the suggested amounts of rake and prebend are for the J boat not the 38. There is no problem with you shooting for the same numbers, but remember the mast on the J 35 IS bendier than yours is-on those boats the mast is adjusted (for main sail shape) ALL THE TIME-and goes from straight to 10" of bend and back several times in a day-the mains for those boats usually have quite a bit of luff curve-my point being that most likely, unless your main has a HUGE amount of luff curve (read VERY FULL) you probably won't need as much prebend as a J35-

To recap: Don't worry about Rake as a "setting"-just use HS length and you get the same result but in a more repeatable format.

You will have to develop your own settings for the 38- and the 35 guide is a good procedure to follow-not so much the actual settings (I think you knew that)...

I probably did not need to say all this-I think we are on the same page by now, but you know me...beat anything to death!!
Seeya,

S

Thanks as always Seth. Do you thing the 1.5" of prebend that the J-35 guide is calling for is excessive as a starting point for the 38? To me it did not sound like much. Aso I am guessing there is an ideal location for the apex of the prebend to be located, such as the middle or lower half of the mast? Finally the j-35 guide talks about being able to take your BS adjuster to 4300lbs. That sounds like quite a bit of tension. I run a 5/16" wire BS. Do you think that tension number is excessive. Again I am looking for starting points to tune from with the goal being by year end having a tuning guide for my 38 that has me hitting the polars.

Tuning

Maybe 1.5" is slightly on the high side-but no real harm in starting there. Is the main fairly deep to begin with? If so, anywhere in that area is OK-you will have to fine tune it anyway once you see it with the sail up.

The Apex of the PREBEND should be right where the the fwd and aft lowers intersect the mast. Once you apply backstay to add BEND (as opposed to prebend), the overall Apex for total combined bend will be closer to the middle of the mast.

4300(max) lbs. is a common number for race boat with rod rigging for the BS adjuster, but yes, it is higher than I expect you will ever use on the 38 with wire. I would shoot for max backstay around 3-3500 lbs and see how the boat reacts. The problem you will have is that the wire will keep stretching under load, so a setting may not hold-but you should notice a gradual loss of tension as the wires stretch-so you may have to chase this around a bit-not the end of the world-many boats have this issue. The solution, if it really bothers you, will be to go with rod rigging sometime in the future.
When I say "reacts , I also mean things like hull flexing, bulkhead/cabinet movement, rudder binding in the shaft. You should be able to carry loads in the 3-3500 lbs range without negative effects (you may see or hear some noise down below, but if it is minor, I would not worry too much). Once(and IF) you notice the rudder binding you know the boat is bending too much, but I doubt you will see this at those loads-I say all this so you know what to look for. The 38 is a STRONG boat, and while I can't recall with 100% certainty, I THINK we often used 4K or so on "Cantata" when the breeze was up-although she had Rod Rigging...

I think you are zeroing in on a good starting point, and as long as the boat is not too loaded with cruising gear, you will hit those Polars. Assuming you have the bottom, sails and deck gear, the 2 things that will keep you from hitting targets are too much weight on board (pots and pans, too many anchors, and in the wrong part of the boat-like the bow, etc.), and not enough crew weight when the breeze is on. A boat like this will need crew weight on the rail in order to carry the amount of sail it needs to hit the Polars. Make sense?

Next?

S

The new main is fairly full but not nearly as bad as the old dacron one... It does respond fairly well to vang and outhaul. I will see what 1.5" of prebend looks like. You are making sense with the prebend apex being where the lowers attach but the bend (from BS adjuster) be a more full arc through the middle of the section. I dont plan on pushing the tension that hard I dont think. I don't really like the idea of binding rudder bearings. We are hauling soon and I am going to shoot Petit Vivid in white on the bottom then polish to 600 grit, maybe finer if time permits. Also installing the max prop then. My headsail (dacron) is in decent shape but the leech and foot covers are stretched out old sunbrella. I am trying to decide if it is worth replacing the covers with dacron to try and improve the sail. Looks like that will run me about $500 if I remove the old cover myself. I think its probably a good idea as it would greatly improve the airflow around the sail as the stretched out wrinkled sunbrella can't be good for flow...

I'm with you-the concern is that if you have too much prebend, the sail will be too flat before applying any backstay. You want the mast set up that you can go upwind in very light air with little or no backstay and have the main not be too flat..too much prebend could cause this-so try it, but be careful. The ideal is go from appropriately full in the conditions above, to BOARD flat with 80-85% of the max backstay you want to use-does this make sense?
I agree about the rudder, but don't be too shy about it. If it happens, just back off-you won't wreck anything-the main thing is to a). be able to control the full range of sail depth with the BS, and b). make sure you can induce and reduce HS sag in the proper conditions. Hopefully, if all is set up right, you can keep the sag under 5-6" as a maximum when pressed in about 18-20 knots TWS. If you can accomplish all this, you have it covered.

If the rest of the genny is really in good shape, by all means lose the sunbrella and replace with dacron. It will be lighter and stronger. The worst case is the sailmaker might have to hollow (scoop) some of the "dead" material on the leech when he applies the new cover, but this is worth it. They should know what to do.

Thanks Seth. I think I will take the genny in to have the covers done. The sail does not appear to stretched out but the leech and foot look like hell from the uv covers sagging. On the tuning I got you 100% and really appreciate you taking the time to discuss this with me. Will update in a few weeks when we are sailing.