All posts by kurt

Fassmer Tender Catamarans- Stuff Done Wrong

Another page on Stuff Done Wrong. These Fassmer catamaran lifeboat/tenders are amazingly bad, in my firsthand opinion.  They were clearly designed by someone who had no experience in catamarans. And the contract must have been huge as there are so many.
Notice in the picture that with only a few passengers, the bridgedeck is already underwater.  It really is a catamaran.  As a lifeboat,it would be OK. You are lucky to be alive. As a tender, I doubt if it could be worse for the job. A tender’s job is to ferry the elderly and infirm from the cruise ship to the shore. Half the passengers had difficulty walking on dry land anyway. The Fass has an ugly combination of pitch and heave inducing features. The bow overhang shortens the waterline, allowing more pitch. (It kind of looks like what a monohull designer thinks a catamaran should be looking like.)   Aft, the draft is cut away for the prop, and that makes pitch worse. The low bridgedeck gets lifted by almost any wave, and the elderly really have to hang on. I was on one in only half meter waves and it was tilting up to 20 degrees, provoking moans from the passengers.
It is only 36.5’ (11.15m) long but weighs 26,455 lbs (12,000 kg). 300 hp gives 10 knots if you are lucky. Even within the envelope requirements, a real catamaran designer could have done so much better.

fassmer

 

Notes on Materials Spreadsheet

The KHSD materials spreadsheet is a very powerful tool to accurately predict what material amounts will be needed in a build. On any design, I query each part of the 3D model for the area of that part, then that is entered into the spreadsheet. I know that the cool kids would build active links between the model and the spreadsheet but I’m not there yet.
This spreadsheet now is the result of years of improvement; hiring licensed naval architects, excel geeks, and just keeping it moving forward. I see even more flexibility and power for it as soon as I get some time. I see extremely complex materials lists linking to another boat parts spreadsheet. When I get time.
A couple of things; I do not count waste in it. I understand that amount to be 20%. I recall that when Sarabi was built, Barry kept accurate records. “your spreadsheet was 20% under” he told me. Yes. You can put a little cell at the end to compute that waste amount.
Along the bottom left center of the spreadsheet are little tabs. They say “master” “plywood”  ”glass lam” “exotic”and  “core”. Click on each one to see the amounts of that type of material. Go ahead and try it. I do often get asked where the other materials are. Try the different tabs.
Not all the tabs apply to you. But they are usually full. I have gotten angry calls demanding to know what all that damn wood is doing on their composite design. Just use the tabs that apply. I have sometimes stripped out the tabs that don’t apply, but that is a mistake. Even after more than 30 years, CM boats are as popular as they ever were. If the plywood is stripped out of a spreadsheet for example, and later needed, it would take hours to replace all of it. So don’t freak out. Just use the tabs that apply to you.
A powerful spreadsheet like this can get a damaged cell just by surfing around on it. A damaged cell can lie to you with authority. Check that regularly. To check for damage, go to any summary cell and right click. It will list the cells that contribute to it and color light all of them up the spreadsheet. If anything looks funny, check it that way.

matmsicap

Weight Studies

One of the most important and vital design tools to create a new cat or tri is the weight/trim spreadsheet. I always use it in tandem with the hull lines program. It’s not that inaccurate to say that knowing how long a boat is does not matter at first. I have my magic hull proportions, and I have weight and payload needed. Ideally, the length is a result. I cannot imagine doing it any other way, but I still encounter builders, even boatyards, who are happy to storm ahead without a weight study. That profoundly amazes me. I know of one professional builder here in my state who prefers to start with hull patterns, and then he freestyles the design from there. Utterly amazing. I even offered one to him for $100 and he declared that he didn’t want to waste his money. (a complete one takes some 10 to 20 hours to flesh out)
Knowing what it will weigh, how it trims, and what it can carry are the most important foundations in any design as I see it. In a series of loops, the hull lines are updated to reflect the excel data. Then the new hull information goes back into excel and tightens that up.
The final hull lines and patterns should only be created after everything else important is designed. Understand that it takes mere seconds to parametrically revise a hull. I know that not everyone agrees with this, but I cannot understand why not.

matmsicap

Spacebag Update

 Vacuum bagging parts with the Space bag has been a mixed scene so far.  It is a wonderful concept, but the bags have been failing.  I started with the 3’ x 4’ jumbo bags.  I am bagging the dome triangles for the lunar lander top.  They are ply/core/ply sandwich parts. Recall that the spacebags let me run the vacuum for only a few minutes, not the usual 6 to 10 hours. The first jumbo bag kept the vacuum for 3 days until it failed.  The second jumbo lasted an hour and the third was good for about 10 minutes.  A smaller XXL bag lasted 2 days, but as in this picture, on a second attempt, the bag would not hold a vacuum.  I tested the closable seams and they were fine.

I spoke to SpaceBag and they will send replacement bags.  They did say the bags should be airtight when you get them and good for several uses with no problems.  I guess I will need to fill up the bathtub to see where the leaks are.  I will do a dry run on every bag in the future to test it first.  Notice the duct tape on the sharp edges to protect the bag.

panel-bagxxl

 

New Launch

A new KHSD 45 has been launched here in Seattle and is now out at Shilshoe Marina. CM plywood/epoxy.  I heard it has an extra layer of 34 oz triaxial over everything for good luck.  Looks nice Marvin.  I do like the color.

marvin45

Composite Bow Bracket

Charles, good chance to show everybody the composite brackets. I think best way to make this plywood bow tube work would be for you to cut one or both of them away, then get the correct space between. Then bond and fasten to deck or hull again. Yours would work fine on an alloy tang model.

bowbracket

Out Next Week

I will be out of the office J7 through J14. Am attempting to get everyone’s things out before I leave. I will update the 2014 Design Book while out. I will also be working on the 3D models of various projects. I will be in Ft. Lauderdale J8 and J9 if there is anything I need to do there.

DIY Plywood Bowtube

Most catamaran bowtubes are alum. or carbon mast sections. Some builders are getting shocking quotes to get these built, so they are considering ply/epoxy bow tubes.
I do urge using the best plywood and do not skimp on construction as this is a mission critical part of your cat.
One thing, ideally the tube end bolt would be not 90 degrees but parallel to the hull. I am assuming the hulls are rigid enough that the delta is not significant enough to upset that pin.

Corners are biaxial roving.  The red is biaxial bushing.  Blue is triaxial.  Yellow is the stainless.  There will be cross laminate to hold the triaxial onto to the box.

PLYBOWTUBEFULLPSP1

 

PLYBOWTUBEPSP1PLYBOWTUBEEXPLODEPSP2

Venturi Vacuum Pumps

I got my venturi pump at Fiberlay. I understand that even though they sell them there, the pumps are not on their website nor in their catalog. They are not wildly net savvy there.
So the venturi pumps are called Vacuum Generators. Part number 1807003 at Fiberlay, listing for $110.50. They pull 27″ of mercury at 90 psi on your compressor. They only pull 2.2 CFM so the vacuum bag has to be good. No moving parts. I’m a big fan of mine. Call Fiberlay at 1-800-942-0660 or find email at www.fiberlay.com.

venturi