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E39 Hull Thickness

gadangit

Member III
Happy New Year everybody!

Recently I had a shipwright (really!) tell me that he thought the hull on our boat was pretty thin. I know for a fact that the hull above the waterline at the V-berth is about 5/16", just like the layup schedule said it would be (ask me how I know.) I also know the hull is about 7/16" below the waterline from installing some thru hulls. He thought that was really quite thin, along the lines of "too thin if you plan on heading out cruising." He was especially surprised that our 42 year old boat was that thin in an era of "overbuilding". But the boat appears to be built per the specs.

I'm having a hard time resolving this in my head. If we pull up to a strange fuel dock, are we more susceptible to a random unseen bolt punching through our hull when it might just make a really nasty gougy scrapy thing on a thicker or more modern hull? Oil canning or other structural flexing comes to mind as well.

I looked back through some old posts and found the comment about fiberglass hulls lasting 10,000 years. It is truly a fantastic material.

I love our boat and have no interest in having anything else. I've just been pondering his opinion. Any thoughts to add?

Chris
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Just "thick" enough ! ?

Some observations:
"Too thin" (and their cousins "just right" and "Too thick") are all semi-meaningless phrases. Even when well-meant, they are still subjective and without real informed meaning that one can put any number to.

And while your friend might certainly be a Shipwright, that old saw about how all the early boats were built overly-thick has been discredited before more than once.

FRP boat building started out in the post war - WW2 - years with small boats and really went big time with trailerable runabouts by the mid to late 50's. Being a smaller niche market, the the early sailboats were indeed (roughly...) modeled on the hull thickness of similar older sailing hulls. By the mid 60's and onwards younger designers with equally modern engineering knowledge were designing sail boats from the ground up for FRP scantlings.

While it would take another decade or two for rampant cost-cutting to really thin out the sailboat hulls to where "puncture resistance" became more of a day to day concern, (Hun__r, to name just one example) your boat was designed in a period where the skin and supporting structure were meant for open ocean use.

Nowadays every builder likes the horizon-invoking ad phrase "blue water" even if their boats are barely safe enough to leave the dock on a 15 knot day. And a bump into any (!) right angle object will indeed fracture or break their skin.

Further, those old time scantlings were not all the same, either. You had single planked with fairly wide spaced framing, single planked with close set or "double" frames, and then diagonal double planked. Plank material varied. I personally have friends with older woodies who are Really Careful never to hit Anything and knock a hole or a split in a plank. And we're talking logs or dock edges that any FRP boat would bounce off of with only a surface scratch. Teak planking was heavy but tougher than the lighter cedar. The variations in construction and strength would fill up a book or two. Or three.

So gather information but do use some filtering. My opinions are still worth only a penny due to the strength of the US$ this week.
Now, when Guy checks in, his knowledge is worth at least a quarter!
:)

Fair winds,
Loren
 
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gadangit

Member III
Some observations:
So gather information but do use some filtering. My opinions are still worth only a penny due to the strength of the US$ this week.

Loren

Hi Loren, thanks for the backstory. Have no fear, I'm an engineer. So I'm used to both being questioned and questioning what I see/hear. So I never take any one thing I hear and run with it. What really got me thinking was that 5/16" is pretty dang thin. Wouldn't have guessed it without seeing the holes.

The video shared by Christian below was interesting indeed.

I'm short gold, so I'll take your penny.

Chris
 

Rick R.

Contributing Partner
That old Crash Test boat sure took a beating for all of us to see. They put holes in it. They turned it upside down. Then after a couple attempts, they blew it up (I think demonstrating a gas leak).
 
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Guy Stevens

Moderator
Moderator
Cored or uncored hull?

The39 came in two versions cored and not cored, which is yours, and where was the measurment taken. I have been on both types, and both are fine for offshore work.

Almost 1/2 and inch of glass is two thin? LOL he must be OLD, as he hasn't been on anything modern!

I have been on and around a bunch of 39's. A bunch of them have been offshore. Plenty strong. Other issues with these 40 year old boats, you bet, hull thickness not one of them.

Guy
:)
 

gadangit

Member III
The39 came in two versions cored and not cored, which is yours, and where was the measurment taken. I have been on both types, and both are fine for offshore work.

Almost 1/2 and inch of glass is two thin? LOL he must be OLD, as he hasn't been on anything modern!

I have been on and around a bunch of 39's. A bunch of them have been offshore. Plenty strong. Other issues with these 40 year old boats, you bet, hull thickness not one of them.

Guy
:)

Hi Guy-
Our hull is not cored. We measured 5/16" above the waterline in the v-berth. I've replaced all the the thru-hulls, removed some and added some. The one core from the hole saw I have laying around is 7/16" thick. Which is about the minimum I've seen in all the locations. Not too worried about that.

Too be clear, I've never been worried about strength. I use fiberglass all the time, I'm a believer. I was just pondering the pointy end of our boat has a hull thickness of just over a quarter of an inch. It gave me pause and I've been thinking about it for a while. Puncture comes to mind as the biggest risk. We've since by default added structure by epoxying in cleats to screw our ceiling boards to. That part of the boat is now stronger than when it was built, but the hull is still the same thickness.

We love our boat, it feels totally solid, it sails great, is sneaky fast and looks like a million bucks.

"Other issues with these 40 year old boats, you bet, hull thickness not one of them." Oh? Do tell...
 

Guy Stevens

Moderator
Moderator
Not a critique just somethings to address

First a photo:
gwImg_0629.jpg

That is my 39 in Moorea, one of my favorite places on our 4 year cruise around the south pacific. She looks a little dirty from all the passages, but was a very comfortable and capable cruiser. One that I recommend for people that want to get out there.

If you are planning long distance cruising, or even some light cruising, these are areas that I would look at from experience, not just on my boat, but on a lot of others.

List of things that most e-39's need to have done.

1> Change out the gate valves for sea cocks
2> Redo the rudder PER THE DRAWING BY BRUCE KING! (After it is disassembled and thoroughly inspected)
3> Most will need their water tanks repaired or replaced.
4> The two mild steel bilge weldments need to be replaced if they are rusted through.
4a> The forward main bulkhead tie together
4b> The mast step
5> The traveler needs to be replaced, ALONG WITH putting some backing plates under it's mounts inside the deck!
6> Backing plates on all the deck gear.
7> AT A minimum the 120 volt electrical system needs to be inspected, about 90% of them were wired backwards, that is the neutral was through a circuit breaker and the hot was a passthrough.
8> In reality the boat needs to be rewired.
9> SS chain plates are well past due for replacement a large job, but it needs to be done. Use ti. (The boat should have been rerigged repeatedly, but probably has not, so this should be done too).
10> Original Hatches need to be replaced by a real hatch.


Beyond that the rest is generally updating and upgrading, but those are what I see as specific issues that need to be dealt with on most of the 39's I have surveyed.

Guy
:)
 

gadangit

Member III
First a photo:
That is my 39 in Moorea, one of my favorite places on our 4 year cruise around the south pacific. She looks a little dirty from all the passages, but was a very comfortable and capable cruiser. One that I recommend for people that want to get out there.

If you are planning long distance cruising, or even some light cruising, these are areas that I would look at from experience, not just on my boat, but on a lot of others.

List of things that most e-39's need to have done.

1> Change out the gate valves for sea cocks Done!
2> Redo the rudder PER THE DRAWING BY BRUCE KING! (After it is disassembled and thoroughly inspected) Done! Also replaced rudderstock and internal metal plate due to inferior replacement at some point in it'd life.
3> Most will need their water tanks repaired or replaced. Water tank is out and in scrap pile. Currently trying to puzzle in new tankage. We had to cut out the cabin sole to accomplish.
4> The two mild steel bilge weldments need to be replaced if they are rusted through. Done! G10 beam installed.
4a> The forward main bulkhead tie together This was removed to enable some head shower pan work. Not replaced (yet?)
4b> The mast step Fine shape, no need to be fixed or replaced.
5> The traveler needs to be replaced, ALONG WITH putting some backing plates under it's mounts inside the deck! Replaced cheek blocks and cars. G10 backing plates glassed in below. The traveler works fine, but maybe someday I'll swap for a more modern one.
6> Backing plates on all the deck gear. G10 plates on all stanchions, deck organizers, cleats, etc.
7> AT A minimum the 120 volt electrical system needs to be inspected, about 90% of them were wired backwards, that is the neutral was through a circuit breaker and the hot was a passthrough. Done! Replaced panel, removed old wiring, not sure how far into the boat I want to bring 120V.
8> In reality the boat needs to be rewired. Done! Well, not complete yet, but new panel is in and wired. New loads are being wired in as they arrive.
9> SS chain plates are well past due for replacement a large job, but it needs to be done. Use ti. (The boat should have been rerigged repeatedly, but probably has not, so this should be done too). Done! Boat has brand new mast, boom and standing and running rigging 2012. All came with boat on the rack, never stepped or rigged.
10> Original Hatches need to be replaced by a real hatch. Done! Bomar hatches replaced the wood ones with a little modification to the opening to accommodate.



Beyond that the rest is generally updating and upgrading, but those are what I see as specific issues that need to be dealt with on most of the 39's I have surveyed.

Guy
:)

We've been busy! Labor of love, but wouldn't trade it for anything at this point. Can we leave for warm clear water now? I already know the answer: not yet.

Chris
IMG_1088.jpg
 
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