Ray, I'm starting to understand your need for speed. I thought I had a death wish for speed, but two wheels are a whole different level of potential bad. Did you race at the national level? If so, we may have crossed paths in the 90's and early 2000's.
We did front-half (Murph frames) the TAFC every year, but most of the problems were with welds and not the actual metal. We also used part of the frame as a puke tank, which helped us know if there were problems. Many years ago, we used a radical (at that time) slip joint on the lower rails that really improved the durability of the whole unit. Unfortunately, it also introduced serious driver control issues, so we disarded it.
The short answer to the question is yes, we are going back with stainless. The two major changes are reduced bend radius and the addition of very hefty gussets.
Compared to mild steel, Chrome Moly can become brittle with repeated cyclic loading.
The Top Fuel and Funny Cars use Chrome Moly but they replace frames at a scheduled interval.
I drag raced Harley Davidson motorcycles for nearly30 years, some with 300 HP, we used Chrome Moly but the whole bike was so light it was overkill, even so we guarded against fatigue cracks by using the frame as an air tank for the shifter, that way we knew if we got a cracked frame, it wouldn't hold air.
Are you going back with Stainless?
The stainless was round (schedule 60 .140 wall) pipe, not tube, and was mandrel bent. Stainless is just notoriously weak compared to good steel. Whenever I see a big boat with stainless anchor chain, I have to chuckle. It's more than double the cost of G43 chain, yet it's load rating is about 40% less. Shiny isn't always best.
I've done a lot of racing, and chrome moly is really light weight, but stronger than the dickens. The sprint car used it, but the real surprise is that it's used in all of the high horsepower NHRA frames. Our TAFC used 1" and 3/4" tubing, and produced about 4000hp. The fuel guys produce 11,000hp, and use exactly the same tube for their frames.
We're building new arms, with a little less bend in them, and 1/4" stainless gussets cut on a plasma table. If those fail, I give up.
Actually round tubes are stronger.
I would go with DOM steel tubing bent over a mandrel, that is what most roll cages are made from, they are betting their life on it being strong.
This one is NHRA legal
It's been a month since I updated this thread, but the month didn't pass without incident.
We finally departed last week to begin our trip up the Mobile, Tom Bigby, Ten-Tom, and Tennessee Rivers to points north. It was a damn short trip.
The davit/lift system we had built was an epic fail. We didn't even make it to Mobile before it collapsed like an aluminum beer can. When it did, it dropped the starboard side of the DR into the swim platform, doing considerable damage to the boat.
For the record, the final lift configuration used arms made from 2" .140 wall cold rolled grade 60 316 stainless. A 700 pound Feathercraft whipped it's ass.
The first photo shows the angle as it was on both arms. The second one shows the additional 25 degree bend encountered when it failed.
Back to the drawing board on the lift. The DR is in the shop, for repairs and repainting the starboard side. Then we'll try again.
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Wow. Why would anyone do that to a FeatherCraft? Indeed, Ray, I think that's too much of a project for me to start. I've mentioned this before, but at my age, it's even unwise to buy green bananas.
Charlie, the strap that's on the boat is very temporary. The canvas shop is making a custom strap that's got fleece padding. They're also making straps for the stern that are the exact length, as a single strap is almost impossible to keep centered on the clevis. I hope they have them done this afternoon, or tomorrow morning at the worst.