Where can I find the Portsmouth modifiers?

It's not the most intuitive navigation: www.ussailing.org -> offshore -> Portsmouth_Yardstick -> Portsmouth Yardstick Index -> Current Tables -> MH Modification Factors

MH Modifiers

To answer your question you take the MN hit

For non-class legal mainsail, of same sail area or less than class legal mainsail (formerly square top adjustment)

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Depends on what boat you're on. The underlying principal is that you follow class rules or take the appropriate modification. Some classes don't require

factory

sails to be class legal like Hobie does. If your sails are class legal with same sail area, there's no hit. If your sails are not class legal, use MN for same sail area or ML for greater sail area.

So, my boats (nacra 20) current rating is only valid as a one design?

If I wanted to change the area of all 3 sails and add beam, would it make for sense to have it measured and rated texel or SCHS(spelling) for the long run instead of basing off of a design that is very different from what it is today?

The short answer is no. I've only seen one race in the US use SCHRS and that was the Tybee 500. Mark S may use Texel in the NE but for the most part nobody uses either system in the US so your measurement cert wouldn't do anything for you.

Personally I think you'd have a ratings beater if you just took all the modifiers applicable in DPN. If there is a weekness/loophole in DPN it's in the modifiers which is the appeal of a frankenboat.

cool! a Franken 20!

How wide are you going on the beam?

How much more sail area you going for?

We have switched in the mid atlantic to SCHRS.... the ISAF measurement system.

I believe the Great Texas also uses SCHRS. The advantage is that it gets rid of the politics in PHRF/Portsmouth.

The OA decides what handicap rating fleet they will offer. If your area jumps to SCHRS... your franken boat would be run through the same rating formula as the stock Nacra 20. Very straightforward... no politics.

Well I am not sure how much I will do, I am still exploring options. At first I was looking at the Open 20 rules but now I have decided against them. I was talking with Randy Smyth about the open 20 and we (I mean he) came up with a sail plan for it. After deciding against the Open 20 we decided that the sails proposed for that class would still be a good choice and he did not see a good reason to go bigger. So my new sails will be a 214sq ft main and a 53sq ft square top jib. So 24sq upwind.

I decided I wanted to try those out before deciding on how much spin area to go with. I think I would like to have at least 2 separate spin sizes.

Beam, again not sure. It depends what options I can come up with for beams. If performance will sell me bare extrusions at a reasonable price, I think I would shoot for 10.5'. If they wont, it will be up to finding some used beams to splice which does not excite me. Carbon beams are not gonna happen.

I want to explore all (if any) options with ratings, because I want to do this mostly just for fun. I love to tinker with things that are good enough left alone, but I want to keep it fair rating wise on both sides.

GT 300 was DPN according to the NOR.

I was thinking of doing all of that stuff, plus curved boards, but couldn't justify the expense. The boards would be your biggest improvement with no handicap that I can find. Pricey but probably worth it. The N-20 always suffered from the fat hull and how quickly it got that way, the curved boards would help get that out of the water. I think your handicap would be 57.5 with the stuff you're talking about doing.

MH Modification Factors
OTHER: Any other deviations from standard class configurations, including the addition of wings, can be assessed a penalty of AT LEAST 0.995. Multiple deviations may incur multiple penalties. Penalties may be greater than 0.995

Then the PN would be 56.9 with wide beams, big main, big jib, different spin (non E/P) and curved boards. Slightly slower (.4) than an RC-27.

Did you ever get a price from anyone on building some curved trunks? Just curious, not something I want to do.

Trunks are easy, the boards are alot of work. F-20c or M-20(would probably come with the trunks) boards would be the easiest and most affordable, still pricey though.For the trunk you just pack the board out a bit, release film, then carbon over your pack. Slide it off the board and you've got a trunk.

I think if I was to do anything like that, I would try canted or L boards. I have a couple extra boards that I have considered experimenting with

a 10.5' width on a 20' boat would make it pitchpole before heel over?

For some reason, I seem to think a boat wider than 1/2 of the LWL has some issue? Maybe some of you designers could chime in here?

There is a point where the additional bow pressure that results from extra righting moment due to the width starts to become a concern....like on the wide supercats (11' x 20'). The additional width gives it better speed potential but it makes them more sensitive to proper downwind handling...and more sensitive to sailing downwind in waves. However, you can control that by being wise with how much leverage you put on the bows...if you're in danger of stuffing it with the kite up, get your crew off the wire and start moving your weight inboard = problem solved. The trick is identifying that you need to do this BEFORE the boat takes you all the way to the scene of the crash. There really is not much concern with this change in the upwind attitude of the boat.

The 20 (at 8.5' wide) is one of the best ocean sailing cats I've ever been on. It will flat out eat waves and wind and you can sail with the confidence that as long as you can keep your weight rearward, the boat will not pitchpole (unless you're out in some REALLY crazy stuff). I think it would live and perform well at 10 or 10.5 feet but it's going to be less wave resistant.

Oh, and BTW, I've got a spare rear beam (standard width) from a 20 that I don't need.

Thanks Jake, I was mostly considering upwind and did not consider downwind effects as hard.

I can see the difference in waves, that said unfortunately for now most of my sailing is on the lakes locally.

seems like a too much work to me (impo)

I would rather just sail it till I break it (or it breaks me), then get another <img src="<>/smile.gif" alt="smile" title="smile" height="15" width="15" />

However, you can control that by being wise with how much leverage you put on the bows...if you're in danger of stuffing it with the kite up, get your crew off the wire and start moving your weight inboard = problem solved. The trick is identifying that you need to do this BEFORE the boat takes you all the way to the scene of the crash.

Jake, coming off of the wire and moving inboard is best to prevent pitch pole? Aren't you taking the cantilever action of your weight off the hull, and loosing the counter balance effect by doing this? Please explain the principle.

Thanks

Forrest
I-20

I agree that it was difficult to truly pitch-pole the N20. It would usually stuff to a complete stop and then flip sideways.

And to Bacho, it does look you've got a great lake boat design with the mods. Guess you don't have to worry much about groundswell

Now, with the larger beam and sail area, are we changing the CE location? Would he need to modify board size or placement to balance the CLR?

Be warned many have gone down the wider beam route with all the trimmings and it has turned into a frankenightmare with big out of pocket. I think if you run the numbers you'll find yourself close to a used F20c!

I don't want to do anything that is not reversible at the moment. What kind of nightmares do you have in mind?

Back in the day a couple of H21 guys went 11 feet wide, which is just a tramp, beams and standing rigging and turned out to be a complete bust but even at that it was a fair amount of cash to get there. The boat simply wasn't designed to be 11 feet wide and it was $$ wasted. They both went back to the 9'6" beam (stock) and never spoke of it again.

Yes exactly. You are losing some counter balance and in order to keep the boat upright, you will be sailing a deeper and less powerful angle. Your speed will drop because the power (and resulting leverage on the bows) will reduce.

I learned a bit about this by sailing the A-cat. The use of the wild thing on a-cats is a little counter-intuitive. There's more to consider with it than just reducing wetted surface area - it's also a method to reduce power and sail deeper. Born out of surviving heavy air (which is quite a learning curve on the a-cat) I learned that keeping the boat flat and sitting on the corner of the boat was not an effective method of safely or conservatively sailing the boat downwind. It's quite the opposite and is pitch pole prone that way. Flying a hull in that position at a normal

skimming the water

attitude was worse now that all of that pressure was reduced to one hull. However, flying a hull high in that same setting finds the boat settling down and becoming a whole new animal. However, it takes a bit of commitment to get it to that point. The additional heeling serves to depower the boat and to make sure it keeps heeling, we scoot more inboard than usual. This also helps to relieve some of the power in the sail and reduce the pressure on the bow. The groove gets pretty narrow but you can manage the heel with the mainsheet and your sailing angle to keep the boat depowered. It's counter intuitive but with more wind pressure, you want to sheet in to heel more and steer deeper. This results in less pressure on the bow while still maintaining a good amount of speed and a great angle. That said, curved boards have kinda changed this game by allowing the leeward hull/bow to resist more power and we're seeing trapezing downwind.

The same, although not nearly as dramatic, is true of sailing a spinnaker boat. You can depower by heeling the boat more and flying higher or sail a little lower with less righting leverage. The trick is to find the best combination of leverage, hull height, and angle. I was getting beat downwind at Tradewinds (18knots) by teams that were keeping their weight just a little more inboard. The skipper was scooting into the hiking strap and the crew, although still trapezed, was more upright. They were sailing about the same speed but a little lower than I. It took me a few races to figure it out and make similar adjustments. Less is sometimes more.

I think it was all that racket your boat was making downwind that distracted you from making those adjustments sooner. Jeeze, watching that video you took made me hit the mute button ...