SailNet Community banner

1 - 20 of 23 Posts

·
Registered
Joined
·
618 Posts
Discussion Starter #1
Just a curious thought.
If you strung a thread across the saloon would you see it sagging and flexing while sailing?
 

·
Registered
Joined
·
8 Posts
Absolutely..l’ve been involved with shaft alignments where we establish a base line by tensioning a piano wire the length of the vessel before she was hauled. Once hauled we could check to see if the vessel deflected. It’s pretty common on larger yachts under certain circumstances...


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
8 Posts
I just reread your question.. could you measure deflection on a sailboat while sailing? For sure, depending on the boat and the conditions- Yes, boats deflect and I’m sure it could be measured. I had an Albin Vega in the 70’s in which bulkheads moved very visible amounts and shifted from one tack to the other...


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
618 Posts
Discussion Starter #4
Very cool with either situation you mentioned. In what direction did the bulkheads move, a twist or just straight movement?
 

·
Super Moderator
Joined
·
4,579 Posts
Sounds like a fun experiment. I would imagine it might be possible.

I think what I might do is tape the string taught between the bulk heads and set up a video camera looking at the string. Review the video footage after the sail and use any catenary in the string to estimate deflection.
 

·
Registered
Joined
·
618 Posts
Discussion Starter #6
Sounds like a fun experiment. I would imagine it might be possible.

I think what I might do is tape the string taught between the bulk heads and set up a video camera looking at the string. Review the video footage after the sail and use any catenary in the string to estimate deflection.
It would be interesting to mount a camera under or over the string as well. That way you could see if there is any racking/twisting of the hull as the string moves off axis.
 

·
Registered
Joined
·
8 Posts
Very cool with either situation you mentioned. In what direction did the bulkheads move, a twist or just straight movement?
In the Vega, there was a panel that was below the companionway which was removable to expose the engine. When at rest, the panel would be touching the sole all the way across, but on a port tack, it would open up about a half an inch on the port side. When we tacked, you could hear-errr,errr,errrck- and the gap would open up on the Starboard side.. it kinda freaked me out. I’m sure the weight of the keel, was flexing the hull. Vega’s were pretty light for their time, about 5000 lbs. for a 23’ waterline boat. Many had crossed the Atlantic, and even circumnavigated- Fiberglass is pretty strong stuff, but certainly a lot of flex is not desirable for the longevity of the structure.

I manage large yachts, and have gone through some pretty extensive analysis to determine why we are getting vibrations related to shaft alignment.. in one case, it was a 142’ fiberglass yacht. There are companies that specializes in this type of analysis. They use everything from piano wire stretching the length of the vessel, and creating a table of off-sets, to digital load-sensors, to lasers..

Do you have a specific type of flexing you want to measure?


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
8 Posts
It would be interesting to mount a camera under or over the string as well. That way you could see if there is any racking/twisting of the hull as the string moves off axis.
That could work, but what about just targeting a laser at a fixed point.. one could mount an inexpensive laser on one surface and record where it landed on a target on the bulkhead. Or mount it on the floor and target the overhead for example...


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
618 Posts
Discussion Starter #9
Do you have a specific type of flexing you want to measure?


Sent from my iPad using Tapatalk
Not really. Im doing some interior work on a old Tartan 34 - moving some cabinetry, perhaps modifying but not removing a bulkhead, re tabbing failed bulkeheads...

It's on the hard, so unfortunately I won't be able to establish a base line to see if any modifictaions stiffen or loosen the hull.
 

·
Registered
Joined
·
8 Posts
Not really. Im doing some interior work on a old Tartan 34 - moving some cabinetry, perhaps modifying but not removing a bulkhead, re tabbing failed bulkeheads...

It's on the hard, so unfortunately I won't be able to establish a base line to see if any modifictaions stiffen or loosen the hull.
Sweet boat! I had a Chesapeake 32 after the Vega.. a little bit similar. (Ok, completely different, but both pretty and of similar size!) I have a T37 on my short list for the hopefully not toooo distant future. The 34’s were very well built.
I can’t imagine much issue unless you were to remove the main bulkheads.. is the rig up? Is the hull well supported?
If she is not well supported, I could see you might lock in some deflection. Do cabinet doors and drawers close OK, now?
If you prepare your surfaces well, all your tabs will just make the boat stronger and stiffer.

Sounds like a fun project!


Sent from my iPad using Tapatalk
 

·
Administrator
Farr 11.6 (Farr 38)
Joined
·
9,380 Posts
On boats from the 1960's and 70's it was not unusual for some of the doors and drawers to stick when heeled over.
I raced on a Tartan that an initiationp prank would be to send the new guy into the head to check something behind the door, and then we would tack trapping him in the head.
I also raced on Morgan 27 that the topsides would spring back to shape when we tacked.
If you want to measure the amount of movement, you need to string a low stretch line on the center line of the boat, and then several crossing the boat perpendicular to the center line and mark precisely where they cross. When you are sailing you can measure the amount of deflection vertically and horizontally. These will be pretty small numbers. The big movements will be torsional, and those are harder to measure since there aren't any frames of reference.
If I was altering anything structural on a flexible boat like the Tartan 34, I would be a very rigid support system before I cut anything out. I would also be concerned about anything that I added which could be a stress riser in a place that was not reinforced for a point load.
Jeff
 

·
Registered
Joined
·
22,716 Posts
an initiationp prank would be to send the new guy into the head to check something behind the door, and then we would tack trapping him in the head.
Great harmless fun. These days, one is expected to provide a safe space to all the young ones.
 

·
Registered
Joined
·
618 Posts
Discussion Starter #14
Sweet boat! I had a Chesapeake 32 after the Vega.. a little bit similar. (Ok, completely different, but both pretty and of similar size!) I have a T37 on my short list for the hopefully not toooo distant future. The 34’s were very well built.
I can’t imagine much issue unless you were to remove the main bulkheads.. is the rig up? Is the hull well supported?
If she is not well supported, I could see you might lock in some deflection. Do cabinet doors and drawers close OK, now?
If you prepare your surfaces well, all your tabs will just make the boat stronger and stiffer.

Sounds like a fun project!


Sent from my iPad using Tapatalk
It's when I get to the gray areas of what is or isn't a bulkhead I have problems. There are obvious paces where they are heavily bonded on three points, (sides), and symetrical port/stb. But you look at the (typical), bulkhead where the head is, and it's not symetrycle, (it would be a solid wall if it was:), and it's not particularly stiff or well bonded, but without a doubt it is adding to the strength of the hull, just not as much as that other bukhead.
The 1/2 wall bulkhead next to stove? I know it's doing more than just supporting a countertop, but what if I wanted to extend the settee? That would require cutting out a section of the bulkhead, which I would only do if I knew the remaining bulkhead would still fulfilling its duties.

And yes, before anything is changed a structural sistering, (or some other method) is in order.

As for the doors closing well and the boat being well supported. It's on it lead portion of the keel, with 5 stands, so..not bad, but not in a form fitting padded cradle that's for sure. The cabinetry is very basic, with huge tolerances, so doors and drawers close and open fine.

And no chainplates attached to any of the bulkheads on mine.
 

·
Administrator
Farr 11.6 (Farr 38)
Joined
·
9,380 Posts
Great harmless fun. These days, one is expected to provide a safe space to all the young ones.
They left me in there for close to 15 minutes. When they tacked back there was a bunch of snickers and jokes about what I might have been doing in the head so long.
I didn't make a big deal about it at the time but spoke to the owner to make sure that it happened to no one who came aboard after me.
Jeff
 

·
Administrator
Farr 11.6 (Farr 38)
Joined
·
9,380 Posts
It's when I get to the gray areas of what is or isn't a bulkhead I have problems. There are obvious paces where they are heavily bonded on three points, (sides), and symetrical port/stb. But you look at the (typical), bulkhead where the head is, and it's not symetrycle, (it would be a solid wall if it was:), and it's not particularly stiff or well bonded, but without a doubt it is adding to the strength of the hull, just not as much as that other bukhead.
The 1/2 wall bulkhead next to stove? I know it's doing more than just supporting a countertop, but what if I wanted to extend the settee? That would require cutting out a section of the bulkhead, which I would only do if I knew the remaining bulkhead would still fulfilling its duties.

And yes, before anything is changed a structural sistering, (or some other method) is in order.

As for the doors closing well and the boat being well supported. It's on it lead portion of the keel, with 5 stands, so..not bad, but not in a form fitting padded cradle that's for sure. The cabinetry is very basic, with huge tolerances, so doors and drawers close and open fine.

And no chainplates attached to any of the bulkheads on mine.
Is this the original Tartan 34 or the later 34-2?
 

·
Registered
Joined
·
16 Posts
Just a curious thought.
If you strung a thread across the saloon would you see it sagging and flexing while sailing?
I sail a C&C Mega 30 OD. A 4,500 pound late 70's ULDB with 2,400 pounds of ballast the hull twists and flexes so much you don't need a string you can watch it flex around the keel lifting mechanism. On rough days you can watch the hull tin can in and out over a 1/4". Pretty freaky when you are trying to sleep looking up and watching the fiberglass flex everywhere.

JJ
 

·
Registered
Joined
·
22,716 Posts
They left me in there for close to 15 minutes. When they tacked back there was a bunch of snickers and jokes about what I might have been doing in the head so long.
I didn't make a big deal about it at the time but spoke to the owner to make sure that it happened to no one who came aboard after me.
Jeff
Seems pretty tame to me. Don't get me wrong, I'm opposed to hazing that causes or threatens physical harm. In the case of your story, it would have been both an "initiation", as you described it, and a lesson on hull flexure and the potential of getting accidentally stuck. You never forgot it.
 

·
Administrator
Farr 11.6 (Farr 38)
Joined
·
9,380 Posts
Seems pretty tame to me. Don't get me wrong, I'm opposed to hazing that causes or threatens physical harm. In the case of your story, it would have been both an "initiation", as you described it, and a lesson on hull flexure and the potential of getting accidentally stuck. You never forgot it.
You are correct that it is a very tame prank, and even in the brief hindsight as I came on deck and realized it was a prank, I thought it was pretty funny.
My issue then as now was with any form of hazing, and my concerns with hazing had more to do with team building and safety. The best crews work together pretty seamlessly, watching each other's back and keeping each other safe. That requires a lot of trust in your fellow crewmembers and their skill sets. It takes a while to build that trust. But beyond that, I am strong believer that there is no place for horseplay on a boat underway, and especially on a race boat, where the boats are being pushed to their limits and the pressure on timing increases the likelihood that mistakes will be made. Camaraderie can be built in a lot of ways on a boat, but I am not a fan of it being at the expense of other members in the crew.

Jeff
 
1 - 20 of 23 Posts
Top