Water Pickup

[gn7]

I have my doubts about material that measures .209. We use a lot of .020 5052 H32 at work.

I never seen a 6061 T6 plate crack back at the turnbuckles.

[SnoC653]

They were on the boat when I bought it. We believe the boat was a K boat or a PS boat before but nobody remembers the fisherman from the Texas coast that used to race it. The 1" transom rod and the cav setup seemed to be done right back for back in the day. To be honest, I just assumed they were 6061 5 gauge but have since been told they were probably 3/16th. The screws were 3/16 stainless fine thread bevel head with lock nuts.

The crack started at the water pickup and than ran pretty straght along the screws for the turnbuckle pads toward the middle. Towards the outside the crack was jagged and moved in closer to the transom. Over all the crack probably measures 7".

Any quick way to determine what type it is?

[WESTERNAERO]

Could have been 6061 but in a t3 condition maybe. Sometimes you can have cracks form from the wrong angle of countersink to bolt fit. If the plates were uncoated and there was a lot of white chaulking going one they could have been 7075 or 2024, more so with the 7075. Getting plate oversized is not uncommon there are tolerances that the mills can use up. +.020 tolerance would put you at the .206 for .1875 plate.
A bad c/s with a lot of vibration would for sure over time fatigue and crack the material.

[WESTERNAERO]

If you think they might have been 7075 pore a little ammonia on the plate, if it turns black there's a lot of zinc and is most likely 7075.

[SnoC653]

If you think they might have been 7075 pore a little ammonia on the plate, if it turns black there's a lot of zinc and is most likely 7075.

Well they aren't 7075 then. I put ammonia and soaked the area between the turnbuckle pads and no black. The plates were painted black and you can see the doubler was also. Paint is worn off/polished off the doubler.

Here is a picture of the crack itself. You can see where it ran along the pressure line from the turnbuckle pad and then started heading to the front edge. This is the bottom of the plate.

[WESTERNAERO]

We're they painted or were they anodized. Anodize fades in the sun like I'm seeing there, and it won't let ammonia or a mind acid react with the zinc. I am seeing a white chaulking corrosion in the c/s holes. That crack looks like the plates saw some trauma and hole to hole was the weak link.
It's kinda funny my old hardware on my boat half of was made with 7075. There's a lot of chaulking on some of the parts. Kinda like these old boat builders were just that and racers on the side. Seems like they would just go down to the local material supplier and grab all the rems of aluminum that were available. Because aluminum is aluminum , right?

[SnoC653]

We're they painted or were they anodized. Anodize fades in the sun like I'm seeing there, and it won't let ammonia or a mind acid react with the zinc. I am seeing a white chaulking corrosion in the c/s holes. That crack looks like the plates saw some trauma and hole to hole was the weak link.
It's kinda funny my old hardware on my boat half of was made with 7075. There's a lot of chaulking on some of the parts. Kinda like these old boat builders were just that and racers on the side. Seems like they would just go down to the local material supplier and grab all the rems of aluminum that were available. Because aluminum is aluminum , right?

I figured it was paint because it didn't cover the edges in the middle. I also sanded an area down and rechecked with the ammonia, no color change. There was definitely a lot of flex going on where they cracked, the doubler has metal transfer from rubbing and a small crack forming as well. The new plates will be 6061 T6 if that is what is prefered these days. I even considered going to stainless since the pedal will have some type of assist on it for racing.

[gn7]

I figured it was paint because it didn't cover the edges in the middle. .

That's because who ever made the plate tried to use a single plate and found out they couldn't get the boat to handle for shit and cut the plate in half.

[Sharp shooter]

We believe the boat was a K boat or a PS boat before but nobody remembers the fisherman from the Texas coast that used to race it.

This may or may not help, but I've never seen a Biesemeyer K boat with 8 turnbuckles. I've never even seen an NRKA Biesemeyer with 8 turnbuckles.

I think the boat was backed into something or rear ended causing the plate to break.

[ogshotgun]

Well they aren't 7075 then. I put ammonia and soaked the area between the turnbuckle pads and no black. The plates were painted black and you can see the doubler was also. Paint is worn off/polished off the doubler.

Here is a picture of the crack itself. You can see where it ran along the pressure line from the turnbuckle pad and then started heading to the front edge. This is the bottom of the plate.

i have seen this exact issue on a boat before in the exact spot...it was damaged from a floor jack lifting the back of the boat up to service the rudder... no need to re invent the wheel .. its metal its old worn out .. replace it.. if the tire on your car gets a slice do you replace the tire or re invent the wheel ???

also that looks like type III hard anodizing also ... fades bad in the sun will lose the color but not the coating and its i believe aout 2-3 thousands thick