Removing forward head compartment bulkhead

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Ixneigh
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Removing forward head compartment bulkhead

Post by Ixneigh »

What happens if I do this? I’ve decided to convert the head space into part of the veeberth accommodations. It’s just a closet on my boat anyway.
If I need to, I can fabricate a deck beam and support that at each end.
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Re: Removing forward head compartment bulkhead

Post by Jimmyt »

The centerboard trunk might serve as a compression post for the mast load. However, the bolted in bulkheads may provide a shear wall type function in the boat, preventing racking. That's typical of frames/bulkheads. Or, maybe not... But, that's the joy of doing structural mod's on something you didn't design.

You could laminate a few layers of 3/4" plywood and build a new, thicker bulkhead. Then, cut out the center out of it, leaving 4-6" around the perimeter. That might give you enough replacement structure and leave you with a more open space. Don't think I'd be comfortable removing the bulkhead(s) without putting something back. But, I'm not a naval architect or marine engineer, nor do I play one on TV. I didn't even stay in a Holiday Inn last night. In addition to being certifiably nuts, I'm a bit of a chicken when it comes to making off the cuff structural changes of any type. I had a structural engineer work out the main support structure in my house. Didn't trust the typical plan drawer/builder/framer method that is typically used in these parts.

At any rate, that's just my opinion. Worth exactly what you paid for it. :wink:

Your boat, your rules. Post pics. I'll hold your beer. :D
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Ixneigh
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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

Ok. A shear wall. I’ll think about that. Has ANYONE here taken that bulkhead out? Could the boat live without it at a the dock? Maybe I could make a flip up and lock bulkhead that is put in place for sailing. The only time I ever had someone cruise with me for three weeks, and we never used the back bunk for sleeping. It’s just too stuffy back there in Florida. I’m going to convert it into a single, with storage for little used items in the far back. (I took out the farthest back pair of cushions) and the larger front bunk would have made a much nicer set up for us. Whatever needs to be done, I’ll do it. My intent is to use the space under the added bunk area for sails, which don’t have a dedicated area now. The plan was for the new bunk surface to hinge upward to allow easy access. I’m tired of having them stuffed in odd places since I use the boat mostly under sail. (Lately the trawler options been looking pretty good though :D :| :|

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KingRichard
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Re: Removing forward head compartment bulkhead

Post by KingRichard »

I did it on my 26S about 5 years ago. If I remember right the top was held in place with a couple of 1/4"-20 bolts that I used a pneumatic cutoff wheel to remove, because the molded in nuts had broken loose. Also, I'm a mechanical engineer, it would appear to have an very little, but somewhat less than zero, structural value. And years later I have no regrets.
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Re: Removing forward head compartment bulkhead

Post by Jimmyt »

Ixneigh wrote: Fri Jan 27, 2023 11:13 pm Could the boat live without it at a the dock? Maybe I could make a flip up and lock bulkhead that is put in place for sailing.
Did some more thinking and checking.

The boat would be fine without it at the dock. I went back and reviewed the Macgregor 26M video and was reminded that the bulkheads are bolted to the liners - not directly to the hull. So, you need to evaluate how rigidly (if at all), the liners are structurally attached to the hull. If you can determine that the liners are basically just floating in the hull structure, then the bulkheads are merely architectural. If the liners are rigidly bonded to the hull, I'd suspect the bulkheads are providing structural rigidity. The daggerboard trunk is definitely bonded at the bottom, and seems to be bonded at the top. So it would resist compression on the cabin top. The loads on the boat structure get hard to envision when you throw heeling, ballast, shrouds, etc. into the picture.

Bottom line, for the bulkheads to be significant structurally, the liner has to be rigidly attached to the hull. Between radiation and hormone therapy meds, I'm not up to crawling around in my bilge today, so I don't know how the liners are attached.

In composite structures, the interaction between components is critical to the structural integrity of the assembly. You can take a piece out and it may be fine for a while, until it isn't. A structural engineer buddy of mine told me about a structure he demolished; and how he marveled at how long the structure stood after knocking out key components. The connections of other elements were able to keep the structure up in spite of main elements being removed.

I'm a licensed Mechanical Engineer, offering advice TO USE CAUTION in modifying your boat's structure. This "advice" is not an engineering product, nor am I practicing engineering of any sort when rendering this "advice". I am not a marine engineer or naval architect, nor should this "advice" be construed to represent an engineering analysis of any type.

Good luck. 8)
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Ixneigh
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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

KingRichard wrote: Sat Jan 28, 2023 7:09 am I did it on my 26S about 5 years ago. If I remember right the top was held in place with a couple of 1/4"-20 bolts that I used a pneumatic cutoff wheel to remove, because the molded in nuts had broken loose. Also, I'm a mechanical engineer, it would appear to have an very little, but somewhat less than zero, structural value. And years later I have no regrets.
Two seconds after I took out the bulkhead and laid it down I had no regrets.
Image



Image

It turns the space into a human sized (barely) bunk. I may or may not extend it across to the other side.
I’m willing and able to do whatever’s needed to restore any lost structural stability. I’ll let the smart people on here suggest how

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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

JimmyT
Thank you for the in depth analysis. That’s why I love about this site.
The liners are indeed bonded to the hull.

Here is my line of thought.
The main resistance to wracking in the M/X/S is gained from the bonded in liner, the ballast tank and the hull to deck joint which brings deck structure into play also in terms of rigidity. The daggerboard trunk and cabin ladder are critical components to tie the deck to the bottom of the boat for overall rigidity. This allows for lighter structure and we all know Roger was all about weight (and cost!) savings. The bridge deck and front cockpit locker bulkheads are also critical members. The two wood bulkheads seem to contribute little, except load transfer for live deck weight (people jumping around) and the one I removed possibly acts as an additional tie the keep the deck from actually moving upward and the sides of the hull outward as the bows bouyancy lifts the boat. In fact, if I lay on my back and brace my feet against under deck, I can push the deck up a bit. Walking on the deck doesn’t seem any different. I’ve put two extra layers of heavy biax glass on the deck behind the front hatch a few years ago so there’s a little extra strength there. I’m willing to do mitigation, and do it the correct way, if I need to.

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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

After some thought, I have decided to use a stainless pipe frame made out of similar size pipe as the entry ladder. It will fit into the funny little grove in the headliner between the two moldings in that location and thus be a little further forward than the old bulkhead. Being only 1 1/2 inches thick it won’t impact space much. The ends, port and strbd, will be glassed onto the hull in the manner with which I usually do glasswork. (Overkill) Given the shear/compression yield of half inch plywood bolt holes, this should arrangement should be far stronger and act as a 2nd athwartships structure that I feel the boat really needs. (The other being the web frame-like arrangement of the forward ends of two cockpit lockers)
I’m sure having that pipe welded up will come at a price…maybe ll ask the welder to sign it.

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Re: Removing forward head compartment bulkhead

Post by Gotro »

Can I state the obvious, trade your :macm: for an X then your resale will stay intact.
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Re: Removing forward head compartment bulkhead

Post by Highlander »

I believe BOAT did a similar Mod on his M check on his mod postings
I would have made the bulkhead a swingaway , lock it in the original position for day time use preserving the head to b used as designed then unlock & swing it open in the evening for night time use as an extended V Berth ! :arrow: :idea:
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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

Gotro wrote: Tue Jan 31, 2023 11:11 am Can I state the obvious, trade your :macm: for an X then your resale will stay intact.
I’ve done a lot of other mods to my boat which I’d have to redo, so trading to an X is probably not something I’d want to do. My boat sails fairly well in real shallow water now which is very important to me.

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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

While a swing away panel was one possiblity, and a good one, I’m also thinking that the additional structure I’d add to replace it would tie in with a possible mod in the distant future if I have the boat that long, where a shorter, easier to manage rig is stayed with a rigid tripod instead of wires. (Possible carbon fiber mast) and in such an arrangement, the front leg of the tripod would need an attachment on the fordeck about there the new deck beam would be.

(This odd rig is a derivative of the lug rig which I had on my v22 and loved it. The mast on such a rig is shorter and might be able to be pushed up into place, and the sail and boom would not need to be taken off. While a 26 foot boat would be the largest I’d want to try the Unicorn Lugrig on, I think it’s feasible given that I rarely sail the boat to weather any distance, and never in rough water if I can at all avoid it. What the rig looses in weather ability it gains in off the wind handiness. The Mac is not ecstatic about weather work anyway)

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Re: Removing forward head compartment bulkhead

Post by Gotro »

I am in agreement with you on sailing to windward. With our out boards it’s just to easy to motor up wind the first leg of the day, then enjoy sailing across or broad reaching home. I have also thought about a shorter mast like a Hobie 16 mast without my back stay and only two shrouds . I. Would have it rotate as well.
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Re: Removing forward head compartment bulkhead

Post by Ixneigh »

The rig I had on my v222 was an unstayed lugrig which I had to do a lot of work to make the deck stronger to support the loads. Plus I needed a mast step on the bottom of the boat. I painted the sail so I didn’t need any covers, which was great. Just drop it and tie it. (The paint worked so-so) and I cruised the boat real world to test the concept and found my patterns actually changed very little. The boat sailed to weather well enough to kick around the bay on a day sail, and any thing more than a few miles, I used the Honda outboard. Just like I do now. I was getting 15 mpg with that rig. (Honda 5 hp) All things equal it was more economical in gas to motor the boat instead of trailer it!!
The M has a lot more windage than the v222 and it’s more work than I want to do to step the mast on the bottom unless the new rig proved to be fantastic. As a dodge to try it out, I devised a tripod brace which would allow me to use the existing mast step and both chainplates. I would just need the forward strut. I want up and down in like five minutes. If I can’t have that then I’m not going to bother. I’ll be taking a hit in sail ability so I’ll want the world in exchange, so to speak.

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Re: Removing forward head compartment bulkhead

Post by OverEasy »

Hi All

Just because a bulkhead panel is bolted in doesn’t mean it doesn’t carry structural loads in either/both tension and compression.
Similarly with liners… that question would be best answered by a proper engineering evaluation.

The deck loads vary by condition…as in people standing…. Mast loads…wind loading…wave loading…torsion….bowing..it all sorta adds up.
Caution is the operative word when removing bulkheads for convenience when the structure is already known to be optimized as in a lightweight sailboat.

In the Mac26X there is a nice tube post under the mast in the cabin to carry compressive loads primarily imposed by the tension of the rigging and stays as well as live loads from people walking about. I suspect there are similar load paths for the Mac26M.

The head liner on the Mac26X also Carrie’s lateral and side-to-side bridging loads.

On the Mac26X there is a post from the headliner to the galley frame for deck compression loading on the port side.
The head enclosure (bolted in) on the starboard side does that same function.
Really wouldn’t want to compromise any of that.

Best Regards
Over Easy 😎😎🐩🐈
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