Thread: Mast Flex question for PDR Lug rig?

With the Oz version of spin tapering there is no mandrel. They use a relatively large diameter tube so there is a big section of tube to push out toward the end of the tube. They start with the minimum diameter end so the re-entrant is as deep as possible. By altering feed rate per revolution they can control the wall thickness more precisely by stretching the tube out more as it spins.

The method was developed by Julian Golding, Doug Harris and Ian (I can't remember his surname) and was microprocessor controlled to control the wall thickness. They all ended up splitting up and setting up different companies with the same tech.

MIK

Interesting, MIK, and could be pointing to the fact that my facts aren't.

Someone told me how it was done years ago and they could be wrong, just like my memory!

Hi Mik and MAM, interesting to see where the balance point on these tapered alu spars is. It sounds like MAM's was made in a way that wall thickness goes up as the spar tapers, given that the balance point is so near the middle.

Interesting Mik that they have found ways to spin a taper while avoiding the thin wall at the bottom/thick wall at the top problem.

My composite spars which have both diameter and wall tapering as you go up have balance points not much above one third the way up from the base.

Ian

Originally Posted by markmilam

AS Regards to Splicing the Alum. mast....I Did use 3 sections of 4in. wide Fiberglass Tape over the 18" splice.....Each section was wrapped Twice and the mast sections had a perfect fit....(I'd rather be lucky than smart any day ) I then sanded the inside of the big Al. tube and mixed up some thickened G 10 epoxy (or G-6, I can't remember) and Slide them together.

Here are the pics. I used pool noodle, and stuck about 2 in. into the top mast section to seal it so it will float....I'll seal the top after I finish .

Hi Mark, it looks like you did a good job on splicing the two alu sections together for your mast.

I do think 18 inches of overlap is overkill on a spar of 2.5 inch diameter, 8 inches of overlap would be plenty and save a bit if weight up high. (The rule of thumb is overlap three times the OD of the bigger shaft)

Ian

The overlap the Laser two piece mast uses would be a good guideline. It is much less than 18". From memory maybe less that a foot.

The join in that case has been proven to be robust. I don't say this to be critical of anything that has happened or other people have used, but rather I try to take successful practice as the standard ... particularly when the sample number is large.

For example ... people talk about the superior performance of the crab claw rig ... based on wind tunnel tests .. but I haven't seen one successful example race around a regular racecourse with other boats over a reasonable period of racing.

Whereas with the Balance lug there has been real experience because me and other people were interested in actually trying rather than basing things on assumptions.

Much more interesting that way.

Sorry to move a bit away from the original discussion but real world practice is always an interesting source of data.

Best wishes
Michael

Agree with Real world Experience.....

The Most important reason for the 18" splice was Laziness .....I had two pieces and I wanted the mast 13'6".....so a 18 in. splice gave me that ....I didn't want to hand hacksaw 2.5 in. alum. tube ......not very scientific, but it did look "about right".

Another question I'm debating is whether to have my Downhaul connected to a eye pad from the mast, instead of the Deck....My thoughts are that the load would be pulling on the mast and not pushing the mast into the bottom of the boat.....just less strain on the boat deck.....does it matter which way its done?? Presuming I'll have a mast pin holding the mast in place anyway, so it doesn't fall out the boat during a capsize.

Ian, I admire your Carbon fiber spars you had made...I'd like to go that way, but for the PDR, I can't find any tubes that would be less than 500.00 or more for a Boom and Yard........unless maybe a old windsurfer mast (cut up) would work, but then I'd be going into a area of unknown Head Flex for my sail, so it may not be that good of a idea........Maybe for a Boom though, I think the boom just has to be strong enough not to bend to much??

Mark

Originally Posted by markmilam

Another question I'm debating is whether to have my Downhaul connected to a eye pad from the mast, instead of the Deck....My thoughts are that the load would be pulling on the mast and not pushing the mast into the bottom of the boat.....just less strain on the boat deck.....does it matter which way its done?? Presuming I'll have a mast pin holding the mast in place anyway, so it doesn't fall out the boat during a capsize.

Interesting point regarding the downhaul load. Sunfish racers add a horn cleat on the mast to tie off the halyard for similar reasons. However, the Sunfish's lateen depends on the halyard to keep the rig and the hull together so the practice is to tie off the stressed halyard on the mast cleat, then run the remainder of the halyard to the deck to prevent separation. You won't have that separation problem with your Lug because your halyard will keep it all together.

Is any of this necessary? I'd ask other Lugs'l equipped OzRacer skippers. Your mast step is probably up to the task of the downhaul. But it probably can't hurt...

Originally Posted by Boatmik

Great reminder MAM. Have you got some pics of the junk rigged boat?

Michael

Here's one scan showing her on the rail at a yard in North Florida:



The junk-schooner rig is unstayed but I kept halyards and spares (for sails and flags) tied off to the lifeline stanchions. In heavy conditions I would rig one of them as a running back stay, tied off to a strong point near deck level.

It is always amazing to see what other people have done!

Wow MAM, wow!

MIK

As soon as my son gets it scanned I'll have one of her under sail. I hope it will be OK to take a slight detour with this thread.

BTW--I was using a wide angle lens to get the whole boat on the rail which caused the illusion that the foremast is smaller than the main. They were both 8 inch OD, cut from 45 foot poles; the main was 44' and was stepped on the keel just in front of the engine. The fore was cut to 39' and was stepped just ahead of the v-berth in the anchor rode locker. The main had about 4 1/2 feet of bury, the fore, 4.

Howdy,

I've always liked when threads head off into other fertile grounds .. so a bit more is great MAM!

MIK

Well, it only took about 35 days.

Here she is under full sail crossing the Bahama banks:



Underway in the ICW:



Some years later, here in coastal Georgia, while cruising with my second ex-wife:

Hi MAM,

That beautiful boat sure looks like one of Tom Colvin's designs, Gazelle? I used it as inspiration for my junk-rigged Wharram cat in the early 70s.

Peter

Yep, a Gazelle with a pilot house I designed and a simplified junk rig, also of my design. It was a wonder boat.