inclining experiment

[scotsman]

i suspect my 41' steel motorsailer is too heavily trimmed by the stern and a big one could come over the stern and downflood into the cockpit and maybe the cabin. will an inclining experiment tell me if the vessel needs to be more on an evern keel to be safe? if not, how would i go about answering that important question? thanks. scotsman

[Ad Hoc]

Do you have a proper stability book for the boat?

[michael pierzga]

An inclination test for righting moment wont be good at identifying weight in the ends. even when floating level an inclination tells little about seaworthiness,

Find out the original design displacement and original waterline flotation before proceeding. Why is the yacht stern down ? Fixed machinery ?

Any sailing yacht who is heavy in her ends is slow , very hard to steer and dangerous offshore in a seaway..

[Eric Sponberg]

Correct, an inclining experiment is a heeling test, not a trimming test. If the boat looks bad by being trimmed down by the stern, it probably is bad. There is too much weight aft. Can weight be shifted forward? You won't be able to easily shift the fixed weights like tanks, engine, and ballast, but what about all the personal gear, equipment and stores? Move as much weight as you can forward, and/or remove any miscellaneous or unneeded gear from the stern to see if the trim comes back level. If it does not come back to level far enough, then some major changes have to be done.

Is the designer of the boat still around and can he be consulted? If the boat is not too heavy to begin with, it is possible that more ballast weight can be added forward to bring the boat back to level trim. The designer may have other insights to the problem and be able to offer solutions.

I hope that helps.

Eric

[scotsman]

thank you ad hoc, michael and eric. the vessel has a big, heavy 3 cylinder gardner aux. diesel and a northstar 7.5 kW diesel light plant aft of midships. there's not much i can do except re-power and maybe put a lot of permanent ballast far forward in the forefoot area, but i'm reluctant to go that route. i have a problem. the designer is no longer alive and i may or may not be able to get my hands on a lines drawing. yikes! again, thanks for the feedback.

[michael pierzga]

Simply sketch a picture of the vessels profile and post. Equipment near amidships souldnt put your stern down far. Perhaps your stern down because your bow light ? Are the anchor chains and ground tackle onboard ? Are you carring any junk aft on deck...tenders ?

[scotsman]

i will have to think about what i'm going to do next. in any event, i won't be able to do anything until march, 2011. i live in ottawa and the vessel is in victoria, british columbia. i won't be there until spring.

IMHO, "downflood into the cockpit and maybe the cabin" should be dealt with as well. A higher coaming? A removable threshold? Close the door? In any event, I believe that there needs to be sufficient freeing port area that the cockpit will near-instantly drain if you ship a wave.

[Ike]

Longitudinal distribution of weight is just as important as transverse distribution. If you are down at the stern you simply have too much weight too far aft. You are right adding weight may even you up but it will put you farther down in the water and displace more, which increases resistance and slows you down. Move weight out of the ends. What's in your lazarette? Where is your anchor and chain? I looked at one yacht that had 20 cases of soda on the flying bridge, and the owner wondered why the boat was so tippy. So first look at where everything is and redistribute stuff.

You may be able to get a marine surveyor or a naval architect to look at it and make some suggestions. If this is a fairly common design the plans may still be available even though the designer is no longer with us.

[scotsman]

mark and ike, thanks. i got it. i've got a naval arch. on the job. there won't be any downflooding and the problem will be fixed.

[mizkuzi]

Hi,
im new to catamaran boat building and i want to ask how much would be the minimum weight and maximum weight to be shifted during inclining experiment? anybody who has a sample inclining report ad datas? just for my reference..thanks so much!

[Ad Hoc]

Originally Posted by mizkuzi

Hi,
im new to catamaran boat building and i want to ask how much would be the minimum weight and maximum weight to be shifted during inclining experiment? anybody who has a sample inclining report ad datas? just for my reference..thanks so much!

Hi Mizkuzi

It is related to the 'expected displacement' and how much lever (distance across the deck) you have available. Since you need to obtain around 2 degrees of list during the expt.

[mizkuzi]

Originally Posted by Ad Hoc

Hi Mizkuzi

It is related to the 'expected displacement' and how much lever (distance across the deck) you have available. Since you need to obtain around 2 degrees of list during the expt.

ah i see, thanks so much for the idea...

[Alik]

Traditional inclining experiment might not be accurate enough for catamaran. There are notes on that in ISO12217-1.

[Ad Hoc]

Originally Posted by Alik

Traditional inclining experiment might not be accurate enough for catamaran. There are notes on that in ISO12217-1.

Alik,

It is not so much as being "accurate enough", but that a cat is very stiff. They give a cut off point of 5.0m for the GM but say it is inaccurate above. But anything with a GM of more than 5.0m...so what if it is 5.1 or 5.5...its stiff!