Aluminum Semi-Displacement Catamaran Build

O C Diver said:

Bkay, your fuel consumption numbers should be displayable on the square screen in real time.

Ted

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I've already got fuel burn set to display. But the boat was hauled immediately after sea trials for punch list work. Other than motoring back to the dock after relaunch, we have not put any hours on her. I should be taking a second trial this weekend to calibrate electronics and check autopilot function and will be able to look at speed and fuel consumption then.

Larmex99 said:

A few new pics from my build. Frames are almost completed and the house will be flipped shortly. At least it is beginning to look somewhat like a boat.

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Hey! You're going to catch up to me at this rate!!

I wanted to wait to comment until I could look at your pics on a large screen. Very nice! One thing I appreciate about Armstrong Marine in Washington is they keep a clean work environment. The amount of debris and flotsam around my boat always bugged me - but that may be the Army guy in me talking.

Short update.

We calibrated electronics Saturday. I should have accepted the boat this weekend but I was told the original builder ordered the wrong electronics, so I ended up without a rudder angle indicator. There's also a couple other issues to address, so I'm holding off until I see how these things will be fixed.

It seems like problems are harder to solve in this part of the country...may it's my imagination.

Performance was acceptable and we recorded 15.6 knots at 2100 rpm burning 6 gph per engine with full tanks. That was a sweet spot with nice wake and comfortable motion.

Problems with pictures. Let's see if this works.

I'm still scratching my head over some things like the companion way doors. I saw them installed for the first time Friday. Thats a tight space to begin with and they are rather poorly thought out. They used a commercial door knob that simply takes up too much of the limited real estate (it's down to a 17" usable passageway). And since the cutouts are already made, all the marine and RV style recessed knobs won't fit. Also, for some reason they didn't feel compelled to include a latch to hold them in an open position. When I brought up being able to leave doors secured both open and closed, the response looked vaguely like a deer in the headlights.

A lot of things like that leaving me scratching my head. I'll see how they address my last 3 open issues and hopefully it was simply Friday afternoon exhaustion setting in. Overall this has been a drama i wouldn't wish on anyone. But I'm still hopeful I'll be high fiving these guys next week when I accept the boat.

Oh, if anyone knows a low profile doorknob that works with US standard holes, please let me know!

Damn, why can't I rotate pictures?

I'm in construction, and the final punch list is really hard on both sides. It is at the end, and everyone is burned out in a variety of ways. Just don't forget that it represents just the last couple of percent of time and money and so worth getting it as right as you can as those are the things that you will probably notice every day... I can't wait to see what the fuel burn is for slower trawler speeds and I wonder how linear it will be from 5 knots to 10 knots...? Also, any idea of the final weight? Thanks again for taking the time to post throughout the project (both the good and the bad).

Bkay said:

I'm still scratching my head over some things like the companion way doors. I saw them installed for the first time Friday. Thats a tight space to begin with and they are rather poorly thought out. They used a commercial door knob that simply takes up too much of the limited real estate (it's down to a 17" usable passageway). And since the cutouts are already made, all the marine and RV style recessed knobs won't fit. Also, for some reason they didn't feel compelled to include a latch to hold them in an open position. When I brought up being able to leave doors secured both open and closed, the response looked vaguely like a deer in the headlights.

A lot of things like that leaving me scratching my head. I'll see how they address my last 3 open issues and hopefully it was simply Friday afternoon exhaustion setting in. Overall this has been a drama i wouldn't wish on anyone. But I'm still hopeful I'll be high fiving these guys next week when I accept the boat.

Oh, if anyone knows a low profile doorknob that works with US standard holes, please let me know!

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Might need some more investigation, but maybe.....

https://www.cheshirehardware.com/croft-1805-flush-ring-handles-chrome-nickel.html

Also, one of these might be adaptable:

https://www.richelieu.com/us/en/cat...ing-doors/privacy-pocket-door-lock-35/1047495

boathealer said:

Might need some more investigation, but maybe.....

https://www.cheshirehardware.com/croft-1805-flush-ring-handles-chrome-nickel.html

Also, one of these might be adaptable:

https://www.richelieu.com/us/en/cat...ing-doors/privacy-pocket-door-lock-35/1047495

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Thanks! I looked at those yesterday and they seem to be for European and Japanese doors. That would be the perfect solution if they hadn't already cut the holes for american knobs.

I'll figure something out. I think I'll start by just making my own knobs.. It just starts getting frustrating when people dont use their heads. I think having a boat built by craftsmen in Maine spoiled me.

I don't have a link, but you might find something workable in "pocket door" hardware.

Ted

Bkay said:

Thanks! I looked at those yesterday and they seem to be for European and Japanese doors. That would be the perfect solution if they hadn't already cut the holes for american knobs.

I'll figure something out. I think I'll start by just making my own knobs.. It just starts getting frustrating when people dont use their heads. I think having a boat built by craftsmen in Maine spoiled me.

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The one pictured uses inches so may be adaptable to your doors.
I would order them and return 'em if you can't get them to fit.

VirtualHuck said:

I'm in construction, and the final punch list is really hard on both sides. It is at the end, and everyone is burned out in a variety of ways. Just don't forget that it represents just the last couple of percent of time and money and so worth getting it as right as you can as those are the things that you will probably notice every day...

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I'm sorry, but I didn't see this comment when you posted it. You are spot on with it. The frustration of a year long delay and transition to a new contractor has pegged out my fun-meter. I genuinely like the guys I'm working with, but they are getting as ready to get this over with as I am. As you say, the details at this point make a big difference, but a person looks really petty and picky when you are at the stage of bitching about door knobs. However, I really appreciate that I can pick up the phone and talk to the owner of the company and have an honest discussion. That's worth a lot!

We had a little hiccup with some electronics (I understand the original builder purchased some incorrect gear which we discovered when calibrating the auto pilot) but after replacing the pump and some black boxes, I am told that's been corrected and the remainder of the punch list is complete. So I'm heading down tomorrow with the intention of doing final acceptance.

Today marks the 1 year anniversary of the original launch date. Oh...and if there is a named storm forming, please dont tell me!

Checking In

I hope you are off enjoying your boat and don't have time to update the forum thread, but can't help but ask if everything is going ok and how you are enjoying the boat. A little more selfishly, I'm interested in your approximate fuel burn at slower speeds, like the 7-knot range, and maybe at the 10-knot range. Best wishes for the enjoyment of your amazing new boat!!!

Huck, quit screwing with me. I'm sitting here drinking a beer and half way through delivery! Can't a guy get a break?

No, actually I appreciate the interest. She's running great and no material issues. I've got a bunch of cryptic fuel burn info and will process all of it when I sit down. But I'll be sure to capture the specific numbers you asked for.

I'm in Coinjock, NC right now and will be home in two days. I haven't had any weather to speak of, so no reports on heavy weather handling.

Great to hear you are on the home stretch to the starting line. Congratulations.


What would be awesome to see is a plot showing fuel burn rate and speed across your operating RPM range in 100-200 rpm increments. That gives a plot of your operating performance across the boat's full range. And from that you can calculate NMPG and range for each operating point.


This data is really useful to have for any boat so you can select the speed, total fuel, and range trade-off that you want for any particular voyage.

Agree with Tanglewood - and then I can add you to my powercat efficiency page . I need to update it anyway as I have lots more data now...

Progress pics for 43 x 16 semi-displacement trawler. House gets attached next and engines will be installed in 3-4 weeks. Expected splash date is early to mid August.

Sorry for the delay. I've been busy making holes in the water.

Here are some general data points on fuel. Most of these are composite numbers from several data points and under various conditions and loads - so they are precisely wrong. I did most of my recording when tanks were between 50% and 75% full.

I didn't waste a lot of time recording much information in the 1500 to 2000 RPM range because she's a complete dog in that range. That's around 8.5 to 11 knots and she throws a ginormous wake. But below that she behaves well and from just over 2000 RPM on up to WOT up she's pretty consistent on NMPG.

600 RPM - 4.22 knots - 7.03 NMPG
1160 RPM - 7.54 knots - 3.59 NMPG
1310 RPM - 7.8 knots - 2.52 NMPG
1800 RPM - 8.47 knots - .82 NMPG
2000 RPM - 12.16 knots - 1.0 NMPG
2100 RPM - 14.97 knots - 1.17 NMPG
2200 RPM - 15.6 knots - 1.12 NMPG
2300 RPM - 17.5 knots - 1.11 NMPG

It seems her sweet spot is just above 7.5 knots for slow cruise and anything between 13 knots and WOT for fast cruise. If these numbers seem really off just let me know and I can make up some better ones.

My delivery was wholly uneventful (if you don't count the lousy prime rib in Coinjock), so I can't say how she'll handle adverse weather conditions. The worst we saw was 3' following seas on the Chesapeake and those were a non-issue. If anyone is curious about how she handles adverse weather, give me a little time then PM me - I'll let you know.

Great Info- Thanks for posting

You have an amazing boat! I hope you can really settle in to enjoy it now. Thanks for posting those numbers, they are really helpful. I might be missing something, but am I correct that this would be considered a semi-planing hull? The way I'm seeing it is that once you get up to 7-8 knots, you are pushing a decent size bow-wave and are in a pretty big hole (getting a bit under 1nmpg), but at 12-13 knots, it gets back on top a little (getting some lift and starting to plane?) as it jumps back up to over 1 nmpg? I'm really good at looking at data and drawing the wrong conclusions...

Thanks for the numbers. It behaves much like my Grand Banks which was a planing hull model. Once it was on plane, the NMPG was nearly constant regardless of how fast you went. It did continue to drop a bit as you went faster, but only by maybe 10%. I reached the same conclusion you did, which go slow, or let 'er rip.

Bkay said:

Sorry for the delay. I've been busy making holes in the water.

Here are some general data points on fuel. Most of these are composite numbers from several data points and under various conditions and loads - so they are precisely wrong. I did most of my recording when tanks were between 50% and 75% full.

I didn't waste a lot of time recording much information in the 1500 to 2000 RPM range because she's a complete dog in that range. That's around 8.5 to 11 knots and she throws a ginormous wake. But below that she behaves well and from just over 2000 RPM on up to WOT up she's pretty consistent on NMPG.

600 RPM - 4.22 knots - 7.03 NMPG
1160 RPM - 7.54 knots - 3.59 NMPG
1310 RPM - 7.8 knots - 2.52 NMPG
1800 RPM - 8.47 knots - .82 NMPG
2000 RPM - 12.16 knots - 1.0 NMPG
2100 RPM - 14.97 knots - 1.17 NMPG
2200 RPM - 15.6 knots - 1.12 NMPG
2300 RPM - 17.5 knots - 1.11 NMPG

It seems her sweet spot is just above 7.5 knots for slow cruise and anything between 13 knots and WOT for fast cruise. If these numbers seem really off just let me know and I can make up some better ones.
My delivery was wholly uneventful (if you don't count the lousy prime rib in Coinjock),

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No need for you to take the trouble to make up better ones. Here on TF we have more than one statistical genius. You can find some of them on the covid sub-forum.
They are so good that they could get you creating fuel rather than consuming it! Well, at least creating hot air and BS which a kinda like fuel.
Ok, I can't even blame having a bad steak for those remarks because our restaurants are still mostly shut!

Nice boat, excellent performance and well done for getting it all finished despite some drama along the way.

If you had said the prime rib in Coinjock was better than poor, I would have been surprised. Probably the most consistently poor meal that people mention on TF.

Ted

Bkay said:

Sorry for the delay. I've been busy making holes in the water.

Here are some general data points on fuel. Most of these are composite numbers from several data points and under various conditions and loads - so they are precisely wrong. I did most of my recording when tanks were between 50% and 75% full.

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Love to hear any more on different weather - I love statistics . When I get to our boat, I'd love to compare (our 50' aluminium power cat).

Do you have any idea of displacement - what the 50% or 75% actually means in pounds (or for those out of the 18th century - kilograms )?

Also do you know your BWL (beam at waterline)? ie. the widest part of one hull at the waterline).

VirtualHuck said:

...I might be missing something, but am I correct that this would be considered a semi-planing hull? The way I'm seeing it is that once you get up to 7-8 knots, you are pushing a decent size bow-wave and are in a pretty big hole (getting a bit under 1nmpg), but at 12-13 knots, it gets back on top a little (getting some lift and starting to plane?) as it jumps back up to over 1 nmpg? I'm really good at looking at data and drawing the wrong conclusions...

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I'd say you nailed it. Around 8 knots the nose comes up and the arse goes down. The best strategy seems to be to simply put the throttle all the way down and when the nose starts to drop and she's in a fairly level trim, then I can back off the throttle and pick the speed I want to travel at. As long as the bow doesn't start climbing back up, I'm fine.

Oh, and regarding the semi-planing - since I have two hulls, I made one semi-planing and the other semi-displacement just to see how it handled. Sorry, that joke never gets old!

mcarthur said:

Do you have any idea of displacement - what the 50% or 75% actually means in pounds (or for those out of the 18th century - kilograms )?

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I just sent the NA some measurements so he can calculate the "as built" displacement. I seem to recall the "as designed" was around 25,000 lbs - but I hope she came out lighter than that. The scales on the travel lift didn't work (and those are usually not that accurate anyway), so if I can get the designer to calculate it based on underwater volume, that would be the most accurate measure.

Also, I have the demi-hull waterline beam calculated from the original plans, but I don't remember the number off the top of my head and I'm away from my house right now. I'll dig that up and let you know.

Dude. That’s an awesome shot of your boat. Congrats on the success!

cardude01 said:

Dude. That’s an awesome shot of your boat. Congrats on the success!

View attachment 104327

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Thank you. I went out with the neighbors in a chase boat for a "photo shoot". Now I just have to figure out how to get pictures and video off their camera and onto mine. I've got my wife on the case - someday I'll see the rest of the pics.

mcarthur said:

Also do you know your BWL (beam at waterline)? ie. the widest part of one hull at the waterline).

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Mcarthur,
Sorry, I neglected to answer this. Waterline beam for each hull is approximately 48". I calculated that from the plan, so its an approximate number, but pretty close.

Still waiting on an as built calculated displacement.

Bkay said:

Mcarthur,
Sorry, I neglected to answer this. Waterline beam for each hull is approximately 48". I calculated that from the plan, so its an approximate number, but pretty close.

Still waiting on an as built calculated displacement.

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Whoops, didn't look closely at my notes. Overall demi hull beam is 48", but beam at designed waterline is 44".

Sorry.