Bluewater vs coastal cruiser - Page 2 - SailNet Community
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post #11 of 12 Old 06-19-2007
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Jeff's discertation is quite comprehensive.
I'd like to add 'simplicity' to the mix.

A boat designed for 'offshore / Blue Water is usually TWICE as strong than a boat designed for 'coastal'.

Typically when you analyse (back calculate) the structural components on a 'coastal' boat you typically realize that the designer has an in-built "factor of safety" of 3; meaning the boat is built three times as strong as it needs to be for 'maximum normal' conditions. For a Blue Water boat, the structural "factor of safety" is usually in the range of 5 or 6 times as strong.

It seems that many designers first conceptually design the boat .... and then mathematically (imaginarily) derive the maximum loading by calculating what load applied horizontally at the top of the mast will result in the boat to be heeled over at 45 degrees ... and then structurally design just about everything in reference to or based on this 'number' AND applying (multiplyng) the appropriate "safety factors" to the structure components. Such 'factors of safety' in design take care of the unknown or unforseen loads that such a boat will encounter ... the historical 'insurance claim' scantlings (actuarial data) of what survived maximum conditions or not has probably led to the 'customary' choice of 'safety factors'.

Obviously it probably gets more complicated than this ... but my back-calculations always seem to arrive at these 'factor of safety' numbers for coastal vs. 'blue water' design.
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post #12 of 12 Old 06-19-2007
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Originally Posted by Melrna
These are just my observations from looking at boats and doing some reading on what generates a Cat A bluewater boat.
1. Hull structure - How the hull is made to take the bending and flexing movement. Bonded bulkheads, stringers and interior pieces to the hull create a stronger hull.
2. Hardware - beefier and attachment points stronger
3. Ports - No plastic here. Ocean waves will create failure of most plastic ports.
3. Cleats - Be strong enough to deploy a drogue or chute without being riped out by the forces.
4. Anchor platform - Beefier to stay on the hook during a blow without bending or failure
5. Stability Curves - Boat be able to right itself in-case of a knockdown over 110 degrees
6. Hull Shape - Be able to ride out rough seas and still be in control of the boat, Ease of motion helps here too. No long overhangs to keep following seas out of cockpit.
7. Rudder attachment points - at least two(top and bottom) - three is better.
8. Deck - being able to clear water over deck fast
9. Cockpit - small to medium with ability to clear water out fast.
10. Liferaft storage to be deploy easily
11. Rigging and chainplates - beefer and oversized. Chainplate attachment points to hull vs bulkhead with beefer stringers to spread the load.
12. Fuel and water tanks - below waterline for more stability. Also in my humble opinion min of 100 gals fuel, 150 gals water for 40' or less boat.
13. Quality of construction of boat.

Just a few I can think of this early in the morning until 2nd cup of coffee

How about boat's an OCEAN boat!!!
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