Aluminum mast size

For Wharram Narai MK IV Schooner Wingsail plans show for wood mast, 6"/ 152 mm dia x 1"/25 mm wall x 34'-6"/10.62m hight . For aluminum mast 6"/152 mm dia x 4-5 mm wall and 34'/10.36m.

I guess number of people make the masts 3' higher to get more headroom under sail foot, will probably will do the same.

Can't find 6'/152 mm x 4 mm or 5 mm wall. But can find Schedule 10 6" pipe, actual dimensions are 6.625"/168.3 mm OD, 6.357"/161.5 mm ID which gives .133/3.4 mm wall.

Available in 6063 T6 and 6061 T6, guessing that 6061 T6 would be preferred since is generally stronger. For a mast the strength would probably be more important than little better saltwater corrosion resistance.

Don't find any mention of alloy recommended for the masts anywhere, so guessing the strength of the masts hasn't been engineered to too fine of a point.

So question is will Schedule 10 pipe in 6061 T6 with 6.625"/168.3 OD, .134"/3.4 mm wall be adequately strong instead of 6"/152 mm, 4- 5 mm wall of unspecified alloy?

I'm guessing the .625"/16 mm larger diameter will compensate for .6 to 1.6 mm thinner wall than plans show. Since being larger diameter makes up some for thinner wall thickness, though i don't know how how much one influences the other.
So I wanted to ask and not just assume on something as important as mast specs.

I figure 6061 T6 would be better than 6063 T6 for mast, Is that correct or are there other aspects that might have a bearing on one over the other for masts? Cost isn't a factor either way.

This is sail plan dimensions in case this info would be helpful to see specs.



Cheers, Allen

 

Many "0ld" mast used 6061 and variations of this.
But there is a much better alloy to use today, 6082, and you would most like have it in the T5 or T6 temper.
T6 is the most common for strength reasons.

Those 'older' 6061/63 alloys are higher in copper content and more prone to corrosion than the much improved updated 6082.
It was developed for this reason, 6082 has 3 times less copper than 6061.

 

Was planning on using Schedule 10 6” pipe because readability available and not bad price.

Would 6082 be readily available and at somewhat reasonable price?

After reading a little, if 6063 T6 would be strong enough for the loads on the masts, it would have better corrosion resistance than 6061 T6.

 

Have you tried making a few phone calls to marinas in your area to see if they have a rack of broken or salvaged masts?It isn't unknown for a shroud to let go and then the wreckage is sometimes kept around as a source of spare parts.Something close to the right size might just be collecting cobwebs not too far away and it would most likely be anodised too.

 

Depends where you source it from, but yes.
Since 6082 alloy is the standard for all commercial aluminium shipbuilding.

 

I'd be concerned with the thinner section with regards to bolting things to it. Can the thinner walls hold the shroud tangs? will it buckle near the mast base - which appears to be a tube that you slide the mast into. This stuff needs to be engineered, not guessed at.

 

They have been engineered to high precision. Wharram designed boats have never failed when built as the plans indicate. Modifications, like making the mast 4 feet higher add a lot of stress to the structure. Google "aluminum mast manufacturers" and you will get many hits. Any of them will have plenty of information.

 

Back to the original question,
Would a schedule 10 pipe, 6.625” OD .134”/3.4mm wall 37’ high mast in 6061 T6 or 6063 T6 be as strong as 6” OD with either .160/4mm to .200/5mm wall 37’ high mast?


Plans don’t say anything about the alloy and simply says 6” diameter and 4-5mm wall thickness.

So just figuring alloy would be 6061 T6 or 6063 T6 as they are by the most common alloys.

If built from wood plans show 6” diameter & 1” wall thickness, built with wood along the lines of Douglas fir and epoxy sealed & varnished.

The wood mast specs give a base line as to what the aluminum mast strength & dimensions would duplicate.

I will try to find 6082 T6, if it is available In similar dimensions as the schedule 10 6061 T6 & 6063 T6.

I want to be as strong or stronger than the wooden mast version shown in plans, since it has more detail specs.

Cheers, Allen

 

I have total trust in James’ designing.
I meant not engineered to be as light as possible and just strong enough vs engineering it to be reasonably light and darn sure strong enough.

From what I understand fairly common to build masts 2’-3’ taller especially on Tiki 38s to get little more sail headroom.

I don’t know anything about the mast sizing and not going to guess that something is ok.

mig 6” schedule 10 will work and be as strong or stronger than 6” diameter, 1” wall wood mast that will by nice.
If not or if not positive it will be then won’t go that route.

If anyone has link or information to find a custom extrusion place I would appreciate it.

Have been looking on line but not successfully, so far.
Whatever I get for masts will be shipped fr mainland, so having a place from mainland make custom extrusion isn’t an issue.
Depending on cost of the masts themselves.

 

For starters I would compare the moment of Inertia, Ix, of the two cross sections. The moment of inertia for your 6.625" x .134" wall tube is 14.4. For a 6" dia tube to have the same moment of inertia it would need to be .1865" thick. There probably is more involved, but so far it looks like your 6.625" x .134" wall tube might work.

In the spirit of full disclosure I am not a naval architect....

 

The wall thickness is an important factor too. It needs to be able to support concentrated loads like the rigging attachment points.

 

Yes I’m asking for help from someone that knows how to figure out if the sch 10 6” is suitable size/strength.

That’s why asking, way out of my field of knowledge.

Wall thickness is .026 less than the minimum of 4mm recommended in plans.



Will be rigging masts similar to this. Nothing else fastens to the masts.

 

I would hope there is a sleeve over that bolt,inside the tube.You may get away with it,but you are reducing the value of the safety factor that was included in the original recommendation.

 

I don't know about the one in the picture, but I will definably put a crush sleeve on the bolts of mine.
Probably be worth turning a short section of heavier well tube to be snug fit to increase wall thickness where the cross bar is also. with fingers cut in it to avoid stress riser, use Sikaflex or similar to bond them together and prevent moisture getting between them.

 

Good to know.What steps are you proposing to take about protection from corrosion?Many masts get painted,if not anodised at the factory.Using a stock tube section this may not be an option that can be applied to the inside of the section.I haven't checked to see how long the cable might be on those very slim cameras that can be connected to a phone's charge socket.One might be a very wise purchase for periodic checking of the state of the interior.