Stability with 5.2 to 1 L/B Ratio

[CatBuilder]

I'm still looking at hull shapes... and I'm looking at long, narrow powered boats. My question is regarding stability and L/B ratios.

I have a specific boat size in mind which comes out to a L/B ratio of 5.2 in a small powered vessel (about 40 feet LOA/LWL)

In order to make this boat as stable as possible, is it customary to put power, batteries, etc... all down low below the waterline, or do you need to add a full length "mini keel" from bow to stern to keep things upright?

Or... am I still thinking too much like a sailor?

Is a 5.2 L/B ratio a stable power boat, if designed to normal power boat conventions? (I realize I haven't given all the facts with weight distribution, etc...)

Lastly, is there a good resource (on the web) to start doing stability calcs?

Thanks.

Originally Posted by CatBuilder

I'm still looking at hull shapes... and I'm looking at long, narrow powered boats. My question is regarding stability and L/B ratios.

I have a specific boat size in mind which comes out to a L/B ratio of 5.2 in a small powered vessel (about 40 feet LOA/LWL)

In order to make this boat as stable as possible, is it customary to put power, batteries, etc... all down low below the waterline, or do you need to add a full length "mini keel" from bow to stern to keep things upright?

Or... am I still thinking too much like a sailor?

Is a 5.2 L/B ratio a stable power boat, if designed to normal power boat conventions? (I realize I haven't given all the facts with weight distribution, etc...)

Lastly, is there a good resource (on the web) to start doing stability calcs?

Thanks.

Am I right to assume that you are asking for a monohull? Your "name" confuses me a bit.

Richard

[CatBuilder]

I know, Richard. My requirements just changed because of the wife. My name no longer suits me at all. Yes, a monohull.

Well I´ve given you some hints on the other thread. Whenyou´re through with that you might have many questions answered already.

Regards
Richard

[Willallison]

It's generally a good idea to always place weight as low as possible. There are exceptions - for instance on vessels with high initial form stability weight is sometimes used to slow the roll motion for a more comfortable ride.

[Ad Hoc]

Also depends whether you have any tumblehome/flare too..this can aid large angle stability

Originally Posted by Willallison

for instance on vessels with high initial form stability weight is sometimes used to slow the roll motion for a more comfortable ride.

There is a comment on Dashews Windhorse site related to that issue. I assume CatBuilder (well, not longer) will still stumble through that site.
I had Jacuzzi´s to serve the motion dampening (not exclusively) on my larger vessels.
Indeed a lower initial stability is preferred on passagemaking motor boats, compared with sailing boats of equal size.