thru-hulls and butt blocks

[redbopeep]

I bet this question has come up and is answered here, but for the life of me (and the wbf advanced search engine leaves a lot to be desired...) I don't see it.

The question is, given a choice of putting thru-hulls at a butt block vs on its own little block somewhere else, which would you think is best?

Our boat had a combination of both (own block and at butt block) and, a couple of our thru-hulls are big enough that I think of them as the equiv. of a plank butt anyway. With the new planking we can choose to relocate those that were on butt blocks (or those that were not for that matter!).

I looked in Chapelle and McIntosh...don't see anything. Figure Pardey doesn't believe in thru-hulls so wasn't surprised when I didn't see anything about it there.

Thanks for any insights.

[Dan McCosh]

I think a butt block is a little feeble to begin with, and adding a giant hole would make it worse. I prefer scarphing to butt blocks.

[oakman]

Well as a counter point I have seen many properly installed thru-hulls lasting quite a long time. By all means not on a butt that is serving its purpose. Thru-hulls should be backed up by a block, I use one that is the thickness of the planking and usually mahogany. If properly shaped and bedded there should be no problem. No extra fasteners needed, though you can use a some screws from the inside if plank thickness allows. I use only bronze thru-hulls so there is more than enough power in the threaded nut to hold all together.

And regardless of what you do, plywood is still a sponge under some coating waiting to soak up water and rot.

Oakman

[redbopeep]

Brian, thanks for your response about your experiences. We had oak butt blocks and thru-hull blocks that were in great shape when taken off the boat. They are all at least 2-1/2" to 2-7/8" in thickness, and overlap adjacent strakes by at least 1-1/2" or more by the way, maybe that helped them last 76 years...

It does seem that EVERYONE has a different opinion on most matters relating to wooden boats. One boatwright we had working on the boat said always use a butt block for a thru-hull if possible. Another said never do so...neither explained "why" they had their position. Another boatwright unfortunately wallows about with opinions either way depending on alignment of the stars.... or if you asked him the question in regards to your boat or his own boat...sincere guy, but hard to take the fellow's advice seriously with all the wishy-washy.

And, as mentioned the boat had both situations: thru-hulls on butt blocks and on their own blocks. A couple of the thru-hulls were on plywood--the boatwrights didn't like that, nope. They were in fine shape, by the way, and probably about 30 years old.

We had (past tense) way too many thru-hulls. Even with minimizing their numbers, we still have more thru-hulls than I'd like. My husband, who knows he'll be the one maintaining internal plumbing, is reluctant to add plumbing to minimize thru-hulls (exception is raw water intake that he's willing to manifold). He likes the simplicity of gravity sink drains, likes having the ability to direct discharge waste w/o pumping when we're offshore, etc. All underwater thru-hulls give me the willies, I'm willing to use a gray water tank and pump it out via an above/at waterline thru-hull just for peace of mind, for example. Since hubby is doing the work, though, its looking like we're going to have more underwater thru-hulls than I'd like...my task here it to make sure they're as safe as they can be.

One of the things that makes me bring up this question is that (minimizing thru hulls) we have a single raw water intake (2") for all systems including engine and genset raw water as well as the drains for the huge cockpit (2 x 2" thru-hulls on each side, 4 total) within close enough proximity to each other and a couple butt blocks that exist in the aft section of the boat for me to think "combining" makes sense. Originally at least one of the two cockpit drains per side was through a planking butt block. Oh, they were 2" lead pipes without seacocks, too.

The cockpit drains can move far enough away from a butt block for me to be happy (using established butt-block spacing guidelines and treating the drains as extra butt-blocks). On the other hand, wanting the raw water filter right at the intake and the whole thing to be very accessible and within close proximity to the engine, we're looking at being closer to butt blocks than we might like OR using a butt block for the raw water intake thru hull. Such are the compromises of life and hence the question put to the wbf regarding this point of butt blocks and thru-hulls.

Thanks again for weighing in with what you did! We did contemplate using plywood butt blocks, by the way. Pretty much seemed that was a conservative way to go. However, we followed the advice of the yard owner /shipwright that replacing in kind with the oak butt blocks would be better for us.

[redbopeep]

Well as a counter point I have seen many properly installed thru-hulls lasting quite a long time. By all means not on a butt that is serving its purpose. Thru-hulls should be backed up by a block, I use one that is the thickness of the planking and usually mahogany. If properly shaped and bedded there should be no problem. No extra fasteners needed, though you can use a some screws from the inside if plank thickness allows. I use only bronze thru-hulls so there is more than enough power in the threaded nut to hold all together.

And regardless of what you do, plywood is still a sponge under some coating waiting to soak up water and rot.

Oakman

Thanks for your response about what you did for your boat. Did you not have a ceiling? With a ceiling, isn't it easier to have the block frame plus ceiling thickness? for good finish and access...

Thanks again. :)

[emichaels]

Bump.

I am hoping for some more people chimming in on this subject as I have 2 unwanted thru holes. Possible three to contend with this month as I wood and paint our boat.

Eric

[Dan McCosh]

To elaborate on my position: I have had numerous problems with conventional butt blocks as starting point for rot. The blocks themselves, as well as the end grain at the butting plank ends. I do't think it is wise to aggravate this with an additional hole, end grain, and issues with bedding a through-hull. Structurally, it probably would be fine, although depending on the width of the plank, an area where a separate backing block is used would be stronger.

[Concordia 33]

I have seen A & R's wood construction. They use butt blocks exclusively (no scarfed seams), but the through-hulls were always on separate blocks. Since I have seen these techniques on boats 50+ years old with no adverse effects, I would lable this a time-tested technique. Some really large through-hulls split between two planks so that the hole does not substantially weaken a single plank with a hole that consumes nearly the entire plank width.

[Gary Bergman]

well, I'm no expert, but...As for unwanted thru hulls, I removed many, and have more to follow, but my perspective is this: I did the last round of removals under CG eyeballs at the time of an inspection, and this was 'appoved' by the inspector...Remove thru hull...epoxy in a proper fitting round mahogany plug (hull is mahogany)...back it up inside by a 6/4 hardwood block, also bolted thru hull. bung all bolt holes. prime, paint, heads all nod in approval...this is the short version, but I think it is understandable..

[Sailor]

Pardey does mention it in Details of Classic boat construction. He recommends you check with the local inspector if you plan to have it certified for passengers etc.

[nedL]

As Oakman said, Butt blocks are for a purpose, and that Isn't for a through hull fitting. Leave them alone. Nothing worng with butt blocks. Use an appropriate backing block for a through hull fitting. (The ceiling should not be included in the picture, it should be properly trimmed away from the through hull fitting.)

[redbopeep]

(The ceiling should not be included in the picture, it should be properly trimmed away from the through hull fitting.)

What I was referring to was that the total thickness of the thru hull block would be the thickness of the frames plus ceiling so that it sits up flush with the ceiling, rather than somewhat recessed. In no case should the ceiling be in front of the thru hull fitting, imo, though.

In our boat, all thru hull blocks were very thick like this--including the ones that were combination butt-blocks/thru-hulls. It made a nice "neat" finished look even though the entire block was accessible.

Given the overwhelming support for having the thru hulls have their own blocks, we've decided to do just that. It means that a couple of the ones that were previously on butt blocks get moved.

[Lou McIntosh]

The question is, given a choice of putting thru-hulls at a butt block vs on its own little block somewhere else, which would you think is best?
...

I looked in Chapelle and McIntosh...don't see anything.

To the best of my recollection -- having heard him using bad language on the subject at various times -- Bud McIntosh believed that plank butts presented enough difficulties (e.g., condensation drainage, end-grain exposure) without complicating the situation by siting a thru-hull in the same place. He also insisted that thru-hulls should be mechanically isolated with (e.g.) rubber hoses so that they would impose minimal mechanical load on the plank they penetrated -- allowing the supporting block to be sized and ventilated so that the inevitable condensation from the thru-hull itself could be evaporated or drained away efficiently to the bilge.

[Lew Barrett]

NO through hull fittings on butt blocks! COMMON SENSE.

A popularly used material for butt blocks (or backing blocks) has become purple heart around here. Through bolted. Tough stuff.
Plywood seems like the wrong product for butts and backing blocks to me. Stable, yes. But it can de-laminate. Solid butt blocks are not at all hard to make, nor are backing blocks for through hull fittings (I need to do one myself for an above the waterline sink drain I installed in a hurry without one). It's hardly difficult work. Everyone with experience that has cautioned against making a butt do double duty here is giving you good advice. If you could, you'd have a boat with no butt blocks at all, but that's not going to happen with fifty foot boats anymore, nor is it possible for making most planking repairs. But I say again; sharing butt blocks with sink drains? FEH!

RBB; glad to see you're doing the right thing by moving through hull fittings off of shared butt blocks!

[redbopeep]

NO through hull fittings on butt blocks! COMMON SENSE.

A popularly used material for butt blocks (or backing blocks) has become purple heart around here. Through bolted. Tough stuff.


RBB; glad to see you're doing the right thing by moving through hull fittings off of shared butt blocks!

Hey, what's with the love of purple heart? I personally don't like it. The purpleheart we've used on floors, stem, and countertimber of our boat has enough little cracks going that I worry about it--and will probably continue worrying about it. Even though we've used tons of boat sauce to keep it from drying too quickly and its clearly not drying too quickly, there are just a lot of little cracks. The oak we've used, conversely, isn't all cracked. Our new oak butt-blocks seem sturdy and hopefully will last as long as the original (77 year old) oak butt blocks did.

Hubby with a couple oak butt blocks:

http://farm2.static.flickr.com/1339/541768201_9068b099b3_m.jpg

[Lew Barrett]

Can't say why yours is checking. It's all the rage now. Tough, rot resistant, strong and reasonably priced. Mine are not checked, but I only made butt blocks.

[redbopeep]

Hubby now tells me sheepishly that he ran outta oak and didn't want to cut a chunk off one of the new engine stringers ...so we've got one (1) purpleheart butt block now...guess I'll have to go lookin' for it :eek: he won't tell me where it is!

[Lew Barrett]

Hubby now tells me sheepishly that he ran outta oak and didn't want to cut a chunk off one of the new engine stringers ...so we've got one (1) purpleheart butt block now...guess I'll have to go lookin' for it :eek: he won't tell me where it is!

Bet it's the last one to give up:p

[Lew Barrett]

I'm sure, in retrospect, that encapsulated ply can work in this context, but why bother? A bit of end grain, even from the bolt hole would be a good place for water to enter. A block made of a rot resistant wood (why I think they like purpleheart) just seems so easy, and in this instance avoids the epoxy step anyway. Butts seem like they are the first weak points in the hull, the first place to get wet from a seam failure. But I'm not as sanguine about ply and epoxy construction as many anyway. Let's say you need a 5/4 butt block. Now you're gluing that up as well. Isn't it easier to just cut a piece of wood, shape and mount it? As to "made to work" they've been more than "made to work." They are one of the building foundations developed over decades, even centuries of sound practice! If your oak butt blocks rotten out in short order,
I'd suspect the materials or the conditions, not the technique if done to best practice. I don't expect to replace Rita's new butt blocks in my lifetime.