Aluminum Semi-Displacement Catamaran Build

Here's a few more shots from Friday.

The first shot is port tank room looking forward into the head. Second shot is port tank room looking aft to the WT bulkhead. And third shot is starboard tank room looking forward into the berth.

Starboard engine room with a John Deere snuggled up in a blankie. Engine will move aft a couple feet and centered on the two stringers visible in the pic.

Here is the companionway into the berth and the platform for a queen size mattress. The platform is on top of the tunnel - so you get exercise simply getting into and out of bed.

The 3rd shot shows the bits and pieces of the berth aft bulkhead. Those are pretty clean welds to my untrained eye.

...and a couple shots of the house now that they have the brow tacked into place.

And finally, the boarding platform.

Very cool! When is the possible completion date?

cardude01 said:

Very cool! When is the possible completion date?

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Yah...that's a pretty good question. I'm told she should still be finished on time despite several milestone delays. Our original schedule has completion and acceptance at the end of May - I just don't see that happening.

I'm hopeful I will accept and deliver the boat sometime in June. I'll be fairly miffed if I'm delivering in July, and I'll be downright PO'ed if it's in August!

Stay tuned...

Genecop said:

That Front end looks awesome, looks like it could drive right over you while swimming, and you would still have a couple of feet to spare..

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Gene, Here's a little perspective shot. Granted, she is blocked a couple feet off the ground here, but at 28" from waterline to low point in the tunnel - she probably counts as a "high tunnel" model.

A couple update shots: Here's a shot of the aft deck before the house was set in place.

...and here's a shot of that one big piece moved on top of that other big piece. Sorry if I'm being too technical.

I'm expecting an updated launch schedule - but at this point I think it's fair to say I'll have a short 2019 cruising season.

How will you manage the noise of the metal hull? Little waves slapping at night.
Amazing build btw. Love love it.

Sea Word said:

How will you manage the noise of the metal hull? Little waves slapping at night.

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Ear plugs...

Actually, that is one of the big drawbacks of aluminum hulls and there is not a lot you can do to mitigate it. We are paying attention to thermal and acoustic insulation, but there is only so much that you can effectively do to get rid of those nuisance noises.

I spent some time on a sister ship and it wasn't as bad at anchor as I expected, especially if wind and waves are coming from the same direction. It was much worse when docked and waves hit the hull from the side.

I've found you can really spend a lot of money on acoustic insulation and get a marginal improvement. I'm going to see how our basic insulation plan works out before deciding whether to start adding more in specific areas.

Yes I’m struggling with this too. I know that spray in foams and bedliner etc would help a lot, but that seems like a one way street and I don’t know that i want to coat the metal with anything unless I have to.

Sea Word,
This is a tough situation. I'm with you that I am very hesitant to start spraying material that you can't easily remove or that prevents inspections. But I realize the time to put that stuff in is when the boat is being built. I am not using any spray in foams based on prior experience with them. But I'd consider some of the paints like Silent Running and some of the stick on acoustic material.

I have a watertight crash bulkhead forward on both hulls. That area is accessible from a soft patch on deck, so that is an area I can get to almost as easily after construction as during. So I might be inclined to put in some type of adhesive material that can help reduce noise, but is removable if I'm hearing the noise from the pointy end.

The main sleeping cabin is my biggest concern because I'm partially above and partially below the waterline. Our thermal insulation should help slightly with acoustics, but I understand thermal insulation is always placed from the waterline up. So this is the area with the greatest chance of nuisance noise transmission.

Aft of that, my tank rooms are below the deckhouse and I hope the acoustic and thermal insulation I have for the deckhouse will help there. I also have watertight bulkheads at the aft end of the tank room. I understand a big part of stopping airborne noise is not having air gaps.

The engine room is primarily under the cockpit platform and it has the greatest acoustic insulation and the least thermal insulation. I'm hoping the distance between engine rooms and saloon and main cabin will help keep the nuisance noise down.

Ultimately, I'm ready to experiment, but want to see where the noise is coming from to avoid slathering the inside of the hull with expensive goops that may not address any real problem.

It looks like you have a "beer can" too. Any tips are appreciated.

Cool yes I’m also anti foam. I also have open V area forward that is sealed from center hull areas. I’ve used the mass loaded vinyl stuff for cars and it does reduce some but not a lot. One thing I’ve noticed on past boats is that the various angles on the exterior makes a big difference. The V berth on our old glas boat swept up at an angle, which met against small wind driven ripples and allowed a slapping. Similarly, our new beer can has spray rails that trap air and allow slapping. So my thought is that this power cat with it’s extremely vertical sides will actually sound a lot less with small ripples at night that can make you crazy. Big waves are still going to make noise but we probably need to expect that.

Interesting, I hope you are right on my vertical sides.

I'm using mass loaded vinyl in the saloon sole to help with the airborne noise transmitted from the engine room. There is a small amount of overlap between ER and saloon. This is my first use of MLV so we'll see if it helps (we are still adding typical ER insulation to kill noise within ER).

My primary concern was manageable noise when underway - that's why we went for engines out under the cockpit.

Well underway I am much less concerned. I like it as quiet as possible at night. Underway, with engines sound-boarding the entire hull, and smashing through the waves of the day, it won’t be nearly as important. But maybe that’s a personal preference thing.

Also with the timeline delays you’ve experienced, just remember that it’s the waiting that is the BEST part! It will be amazing, and the longer it takes, the more you’ll appreciate it. At least that’s how most people are wired.

I still regret letting that alloy power cat go 20 yrs ago.....

I’ll snap a pic of the twin power cats that the army corp of engineers operates out of the river just by my house. There’s usually only one or none in dock, but they are very similar to what you’re building. And I’ve LUSTED after them for a log time too. They might be a little bigger or at least beamier but they just sit so STANCED in the water I love them.

Despite some of the comments above, waiting on a boat is not my favorite pastime. I enjoy the problem solving but I try to let the experts work without too many interruptions from The Good Idea Fairy.

But here's one I screwed up in the design stage - the transom boarding steps were 18 inches. I thought that was sufficient until I actually saw them in real life and smacked myself for not making them 20 - 22 inches. I didn't want to keep extending the size of the boat - but I should have given myself a little more room here.

As a compromise, the I asked how we could place the railing to maximize step space and they came up with tabs welded on the transom. That's one benefit to aluminum (and steel), if you need to make a change, just cut off the old one and weld on something else.

Gunwale boxes for house battery bank to port and storage to starboard. There is an engine room air exhaust at the aft end of these boxes.

I'm not keen on having battery box on deck - but they will be easy to get to and easy to service. And I'm sure when I'm 60 and replacing batteries I'll be happy to not have to lift them out of the bowels of the vessel.

I've also been debating raw water intakes. I've seen aluminum workboats use a standpipe in order to keep the seacock above the standing waterline. I'm using Marelon seacocks and they have a lot of pluses and a few minuses.

Two big drawbacks is that they are more susceptible to freezing in an open position than bronze, and some of the older units had handles break off. That latter problem has supposedly been corrected by beefing up the handle, but when they broke off a small amount of water trickled in and you had no way to close them.

If you can mount seacocks so they are a hair above the waterline at rest, you alleviate both of these issues. You still need to close them when not in use, but they are not submerged in water and become difficult to operate. Also, I don't believe Marelon seacocks have a drain plug, so if you winterize in the water there is a small amount of water trapped in the ball. Forespar tells me they have never had one damaged in my climate because of water freezing inside it - but again, having it above the waterline negates this problem as well.

The key to this working is being able to design a standpipe that has enough support to resist the lever forces AND resist vibration that could cause a failure in welds. The owner of the company appreciate the idea of the standpipe, but was not sure they could design one he was happy with.

I asked them to give it a shot and the production engineer has confirmed that my raw water pump is self priming (I didn't even realize this was an issue) so they are working on a sturdy, workmanlike design for a standpipe. I guess there will be more to follow on how this shakes out.

The fact that the stand pipe is aluminum and in contact with water should be sufficient to prevent freezing

Hey I just saw this build. VERY COOL, keep the progression photos coming!! This stuff fascinates me. What engine(s) are you putting in it?

Bkay said:

Some very tangible progress! There are now two engines with reverse gear sitting in the shop! I grew up working on John Deere tractor engines and these are the first two JD's I've ever owned.

As much as I hated working on his engines as a kid, I'm sure my dad would be amused to see me buy two of 'em.

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Just saw this so ignore my previous question, now I know John Deere’s!

Bkay, not sure if it’s been mentioned but another member is building an Aluminum LRC in Turkey currently. They keep a very comprehensive Blog of the build and address sound deadening etc..Google Mobius World....

Genecop said:

Bkay, not sure if it’s been mentioned but another member is building an Aluminum LRC in Turkey currently.

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Yes, I've seen that and I was in touch with Dennis Harjamaa, the designer of that boat, back when I was in the planning stage. Dennis was very helpful, but just didn't have time to consider a new project.

He's a good guy, I'm happy to see his boats getting some love.

JMK2000,
Thanks, and consider your question ignored!

Bkay said:

Despite some of the comments above, waiting on a boat is not my favorite pastime. I enjoy the problem solving but I try to let the experts work without too many interruptions from The Good Idea Fairy.

But here's one I screwed up in the design stage - the transom boarding steps were 18 inches. I thought that was sufficient until I actually saw them in real life and smacked myself for not making them 20 - 22 inches. I didn't want to keep extending the size of the boat - but I should have given myself a little more room here.

As a compromise, the I asked the guys as USWB how we could place the railing to maximize step space and they came up with tabs welded on the transom. That's one benefit to aluminum (and steel), if you need to make a change, just cut off the old one and weld on something else.

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why not just add a bit of overhang like swim step style? Wouldn’t look bad, would add to oal though.

Sea Word said:

why not just add a bit of overhang like swim step style? Wouldn’t look bad, would add to oal though.

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That's a good idea and it was my second option if I didn't think the rail-on-the-transom option would work.

Here's a couple update photos from my inspection last week:

Here's a couple shots from the helm with a big ass ferry bearing down on me! The 3rd shot is the companion way into the cabin.

Here's a shot of the port side deck before the steps are installed.

That second shot is the access to the side deck as seen from helm. I obviously would have preferred deck access right by the helm, but that would have required moving the helm back (and losing visibility) or losing my access down to head and cabin. This was the final compromise.