Nacra 5.5sl Mast Post Question

My mast post has all kinds of thread space to make adjustments up and down but I can't find any information in my assembly manual to tell me how or why to adjust it. Is it supposed to be adjusted downwards to give the dolphin striker some pre-bend? Or can it be used to raise the mast and tension the shrouds some? (doubt it).
While I'm on the subject the mast post on my boat doesn't even touch the dolphin striker (although I've not noticed if it does with the mast up) but I did noticed, from looking in the murrays catalog, like I'm missing a piece that goes between the mast post and the dolphin striker..... a support pad. What is this all about? I know the boat didn't come with it. IS it critical and should I not sail it till I replace/repair that pad? Thanks for any assistance you can give. Love pictures if you have any of what it should look like. Tried to do a search and also scan Patricks Nacra website but couldn't find a clear shot of the issue.

Greg

Yes, the pad is critical. It keeps the post from punching through the dolphin striker strap. The post should be adjusted to produce 1/4" to 1/2" of upward bend in the main beam, when the boat is unrigged. This lets it flex back straight under the compression load of the mast. I may be slightly off on the exact amount of prebend; I'm sure someone will chime in. Good luck.

Andrew, I am just off the water and still shaking my head.
I took what you said and it sounded perfectly reasonable so this morning I fashioned a pad to keep the post from punching a hole in the dolphin striker. And went sailing.
Two hours later we hear a loud BANG!!!! The mast ball is just visible above the front beam. The mast coupling is still covering the ball but the shrouds are loose as hell and I'm scared we are going to de-mast. I put the captive pin back in by pushing the rod back up as much as I can till it seats nicely in the mast cup. The dolphin striker is in perfect shape but the post has slipped down next to it giving the post some stability. We limp in carefully and take everything down as slowly and safely as possible and then go investgating. The top nut that usually rests above the beam is now inside the beam. As I look more closely now at the COMPLETE MAST STEPPING kits for sale on Murrays I see that I should have had both a compression sleeve AND a washer between the two nuts. Both were missing when I bought the boat.
SO now I have a front beam with a hole blown through the top the size of the nut. I've got a couple of people checking on getting my a new front beam but sitting here wondering and trying to learn from the experience I'm wondering if something bigger than a washer should be under that top nut to spread the load. Under load that is a lot of weight. I also wondered if this beam is trash or whether a 12-14 inch piece (of something solid with the same outer radius as the beam) could overlay the hole and be drilled to allow the mast post to come through and also riveted into place to repair the damage done by me today.
Is that just stupid? In hindsight the whole accident is stupid and I'm kinda embarrassed I didn't recognise the problem and correct it before it happened. I guess everything in hindsight looks stupid but still.......

I'd love to know what you experienced sailors think about all this. I also wish the assembly manual supplied by Performance showed in some detail (instead of ignoring it altogether) just what that critical area (the mast post)should look like. The manual doesn't even mention the components of the post nor how to adjust it to give some prebend. NOTHING. The only place prebend is talked about at all is on the bridle.

Well, we survived and after a few dollars more we'll be back at it. Wiser and poorer. Hey anyway, the great news is my crew/wife and I flew our first hull today. Wahoo!!!!!
Thanks folks!
Greg

Sorry this is a little late but that little aluminum casting that should rest between the mast post and the dolphin striker is to keep the mast post centered on the dolphin striker - to keep it from slipping off to the side as just happened. The dolphin striker (truss) should carry most of the load from the mast and as Andrew said, mast post tension should be adjusted to get a little prebend in the main beam. This ensures that the dolphin striker is carrying the majority of the mast load.

You're right that there should be a compression sleeve (although it's not terribly thick) inside the beam. If the beam had a flat top, I would consider putting a plate on top to provide structure over the hole. However, this would not work very well on the round beam. You could, however, go to the trouble of forming a piece of 1/8" to 3/16" aluminum plate to fit closely around the curve of the beam and restructure it that way - but a replacement beam would be less trouble.

Thanks Jake. Your reply does answer a lot. How does the little aluminum cast actually remain on the dophin striker to keep it centered? What adheres it to the dolphin striker. It must be more than friction.
I hear what you are saying about easier to buy and replace the front beam but it sure sounds less expensive to form a curved aluminum "patch" out of 3/16 aluminum (provided I could find someone to do that or figure out a way to hammer it out into the right radius. Hey, maybe my local neighborhood blacksmith -two doors away might have some ideas) If it were riveted in place to provide lateral stability and the rest of the post resting on the dolphin striker provides vertical load pressure I'd be in business again. Wouldn't I?
To go the new beam route,...any good ideas where to go for that beam. Sailing Pro Shop? Rick Bliss at New England Catamaran? The online store at this forum wouldn't be able to do that would they? Would a used beam be possible or advisable?

Thanks again Jake. Ran across that awesome picture of you (flying a hull going away from the camera on the thread of which boat to buy) and it seemed as if your daggerboards are extraordinarily long. Are those standard boards on your boat?

Regards,
Greg

Yes, those are standard Nacra F18 boards. Hobie Tiger boards are very similar. They are a little fatter and shorter than the Nacra 20 and Nacra 17 boards.

A while back, Rick Bliss had a couple of front beams for a Nacra 6.0 - I believe they are the same. One was rigged with hardware and the other without. You should give him a call. A used beam would likely be fine but you may want to make sure that it doesn't have extensive corrosion.

The cast aluminum piece is in a slight "V" shape to match the dolphin striker. It is slightly wider than the dolphin striker material and has a ridge in front and in back of it to keep it centered on the dolphin striker. It is slightly hollowed out on top to fit the mast post. The pressure from the mast post and the fore and aft ridges keep it in place on the dolphin striker. No adhesive is required. Two photos attached.

.

Be sure to use white lithium grease on the threaded hardware when you reasemmble the front beam. This helps to slow down the galvanic reaction between the stainless hardware and the aluminum beam.

That's terrific. The pictures illustrate the relationship of the dolphin striker and the piece perfectly. Apparently, that crucial piece was missing when I purchased the boat and I didn't know enough to realize it. While I was typing this the Sailing Shop called and said they have a new front beam in stock for $ 575 plus shipping but I think I might give Rick a call in the morning to see what he still has and pick his brain a little. I think a good used one would be fine in my circumstances.
Thanks again for the tip, I'll remember to use the lithium grease.
Regards,
Greg

the Nacra parts catalog and 2001 pricing guide (note this is pretty old) state that a fully assembled 5.5sl front beam is $525. There's not much more detail, but that probably includes EVERYTHING - like mast post, dolphin striker, hardware, beam straps, beam bolts, etc. You just need the aluminum extrusion that is drilled for the major components. Also of note is that the catalog lists a different part number for the 5.5 uni and 5.5 sloop front beams - although that's probably only different because of different hardware configurations.

I saw that Jake and I wondered just what "complete" meant.
I've got a call into Rick Bliss and I'll see what he thinks but I also figure I have not much to lose to try and repair this beam sufficiently well to use it. Here is what I'm thinking.......
I bought a piece of Aluminum Angle that is 1/8 thick. I'm going to stop in at the blacksmith shop and see if he can pound it into a reasonable arc to match the beam. As it is it covers the hold made by the nut pushing through the beam.
Then I thought I could coat the area with RTV or equivilent and stainless steel rivit it down to secure it. I've got enough room between the barberhaul camlocks to put in a piece about 20 inches long that will give me lots of room to put in 4 or so rivets on each side of the hole.
What do you think of that? After I drill the hole for the rod and mount it this way do you believe that I will have sufficient lateral strength to secure the mast in place? If anything the 1/8 inch material is A LOT more substantial than the thickness of the beam wall itself so my thought it this might be even better than the original set-up if I can secure the lateral movement side to side and fore to aft. I would think 8 rivets would lock it right in place. You?

Thanks for your support!
Greg

Greg,

That sounds pretty reasonable to me. Just be sure to debur the edges so it doesn't become a skin hazzard!

JAKE! Even better. I stopped and had a reinforcement welded onto my trailer a few minutes ago and asked the welder if he could do anything with the aluminum beam and he said, "Sure no problem. Make it stronger than before." They can bend a piece of 1/4 inch aluminum plate and shape it to the beam and weld it all the way around. $ 60 plus the piece of aluminum. It'll take them an hour and I can have it done tomorrow. 8:00. I'll take before and after pictures and post tomorrow. Wahoo!!!! I'm sailing again tomorrow!

Don't forget the comprression sleeve inside the beam and around the post! This is very important.

Great point Les. When installing the rod into my new-and-improved beam I guess I shove the rod up through from the bottom (with the bottom nut and washer already in place), then slip the compression sleeve down over the rod and through the hole in this new plate so that it fits INSIDE the beam and then washer and nut and ball complete the installation. Is that right or do I have to figure a way to slide the compression sleeve through one end of the beam till it aligns with the holes and then I slide the mast post up through it? Here is why it is important......
I need to tell the welder how big to drill the hole through the patch. Big enough for the rod only or the compression sleeve? Can you tell me the dimension of the compression sleeve? (I ordered a new complete mast rod assembly with the missing compression sleeve AND dolphin striker piece that holds the rod but it hasn't got here yet to measure).

Thanks guys.
Greg

I have a few beams for 5.2s--if the 5.5 uses the same beams, you could just replace the whole thing with a used set-up a lot cheaper.

Contact me at danberger@mindspring.com for more info

I've not ever taken the compression sleeve out but I'm pretty sure it will not fit through the hole in the beam - hence it would have to be installed from the end of the beam (taped to a batten or something).

A couple of things.
The Main Beam (front crossbar) functions as a truss with the vast majority of the vertical mast load being supported by the tension member, the Dolphin Stryker V-Bar.
The lateral forces are controlled by the holes through the Main Beam.
The Dolphin Striker Casting is held in place by the pressure(pre-bend) from the Dolphin Striker Rod.
The Compression Tube prevents this pressure from collapsing the Main Beam.
Unfortunately, pre-bend reduces the height of the Mast Ball above the Main Beam.
This can cause problems with the clearance between the Mast Base Casting and the Main Beam during mast stepping.
I have seen some Mast Base Castings gouged by the top Dolphin Stryker Rod nut.
Adding a plate to the top of the Main Beam will further reduce the limited clearance.
Hopefully, you will have enough clearance on your boat

I would use a temporary bolt to hold the new Compression Tube in place and to pull the new plate in tight to the Main Beam while it is being welded.

P.S.
I think the 5.5 is 8.5' wide, but the 5.2 is only 8.0' wide so the crossbars won't work.

I taped the compression sleeve to a piece of 3/4" PVC pipe (in a T configuration) long enough to reach the center of the beam. This allowed me to be able to slide the compression sleeve in from the end and position it so I could drop in the threaded mast base rod. Then just pull hard and rip the tape loose.

Regards,
Mike

Well, that is certainly a great idea BUT I don't have the compression tube (it was missing from the boat when purchased as was the Dolphin Stryker casting) and the newly ordered one won't arrive in time for the patch welding tomorrow. I like the idea though of using a temporary bolt to hold the patch down during welding. I'll suggest that to the welder. Since I'm only adding 1/4 inch to the height of the main beam I hope not to interfer with stepping the mast. It's possible, I guess, but we'll have to see. For now I'll plan on adding the compression tube after the fact through the end as a couple of guys have suggested.

Here' s a couple of additional questions....

How EXACTLY do you measure the pre-bend by the way? A couple of full turns of the bottom nut after first touching the casting?

Do you think the fact that the new compression tube will be slightly short than typical (shorter by the thickness of the beam wall when positioned between the inside of the main beam and the patch) will make any difference at all?

Thanks,
Greg

Here is a BEFORE photo of the damage....