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.

[apex1]

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.

[apex1]

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

[apex1]

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.