What is the magic beam for a cat

[Seapig]

Everyone makes good points. The issue is one of practicality. I want a boat that has a 16 foot beam on the outside and a 30 foot beam on the inside. Lacking TARDIS technology I will have to compromise. Auspicious makes an excellent point. The well here tapers so that they could haul a 25' beam boat as long as it was only 20' long.

As I am looking for a "magic number" I don't expect to get anything exact, just impressions. I would interpret Escape Plan's number to be 23. Auspicious 23.5. NortonCove would seem to think 20.5 but he's from Newfoundland so by definition he is crazy. My family is from the rock so we may be related. MyCatLife's wife may have the same kitchen appliance proclivities as my wife.

Thank you again for your thoughts.

[Auspicious]

Originally Posted by Seapig

The issue is one of practicality.

Which reminds me of another practical issue related to haulout and thus to beam. With the proliferation of sail drives the service life of the lower seal is critical. I delivered a Lagoon 38. The service life on the lower seals was only 100 hours. Fine for daysailing near home but totally inadequate for cruising. You have to haul out to replace the seals! Unless you can count on beaching the boat in an area with substantial tidal swings and can move promptly you are dependent on regular haulouts.

[Steve_C]

Originally Posted by Auspicious

Which reminds me of another practical issue related to haulout and thus to beam. With the proliferation of sail drives the service life of the lower seal is critical. I delivered a Lagoon 38. The service life on the lower seals was only 100 hours. Fine for daysailing near home but totally inadequate for cruising. You have to haul out to replace the seals! Unless you can count on beaching the boat in an area with substantial tidal swings and can move promptly you are dependent on regular haulouts.

Not sure about older saildrives, but i have scoured the manual for my sd60's and there is no mention of a service interval of 100 hours for the seals. Oil change interval for the saildrive is listed at 250 hours and its equipped to do this from above while in the water.

[Auspicious]

Originally Posted by Steve_C

Not sure about older saildrives, but i have scoured the manual for my sd60's and there is no mention of a service interval of 100 hours for the seals. Oil change interval for the saildrive is listed at 250 hours and its equipped to do this from above while in the water.

These were small Yanmars. 35 HP? I don't remember for sure. It all appeared when the owners promised maintenance but didn't. One sail drive seized between St Thomas and Annapolis. That was only one of a number of missed maintenance items on that boat that bit me.

[teneicm]

So we're pretty beamy (26 ft) for our LOA (48). It means that we need either a 75- or 100-ton travelift. 50 ton travelifts seem to be the most common, so we do need to look around a bit, but we've always been able to find options. One thing that I won't be doing again is an under- bridgedeck lift. I don't like the stress it puts on the boat as the hulls just hang unsupported off the lateral beams.

[blubaju]

I wouldn't sail any catamaran if there is any doubt the hulls will fall off on a calm day. What about the loads in a rough sea?

[Tupaia]

Originally Posted by teneicm

So we're pretty beamy (26 ft) for our LOA (48). It means that we need either a 75- or 100-ton travelift. 50 ton travelifts seem to be the most common, so we do need to look around a bit, but we've always been able to find options. One thing that I won't be doing again is an under- bridgedeck lift. I don't like the stress it puts on the boat as the hulls just hang unsupported off the lateral beams.

Our 28ft beam (LOA 44) makes most travel lifts incapable of lifting us (150-300 ton). A trailer, syncrolift or railway bogie under the bridgedeck is much kinder and doesn't require rub-rail protection. As we have no keels being chocked under the bridge-deck is also preferable giving access to completely sand and anti-foul the hulls.

I would be very wary of sailing a cat that could not be supported under the bridgedeck

Nearly all French production cats built around La Rochelle are delivered like this on a special truck.

[redneckrob]

Originally Posted by Auspicious

Which reminds me of another practical issue related to haulout and thus to beam. With the proliferation of sail drives the service life of the lower seal is critical. I delivered a Lagoon 38. The service life on the lower seals was only 100 hours. Fine for daysailing near home but totally inadequate for cruising. You have to haul out to replace the seals! Unless you can count on beaching the boat in an area with substantial tidal swings and can move promptly you are dependent on regular haulouts.

Memory is a tricky little sucker. I'm going to be blunt and just say your memory failed you utterly and completely on this little item. There aren't any sail drives anywhere that I am aware of with a 100 hour lower seal life, and most certainly not on Lagoon 380s (there also isn't a Lagoon 38 model, so I assume you must have misremembered that as well and were thinking of the Lagoon 380).

[Auspicious]

Originally Posted by redneckrob

Memory is a tricky little sucker. I'm going to be blunt and just say your memory failed you utterly and completely on this little item. There aren't any sail drives anywhere that I am aware of with a 100 hour lower seal life, and most certainly not on Lagoon 380s (there also isn't a Lagoon 38 model, so I assume you must have misremembered that as well and were thinking of the Lagoon 380).

Maybe. The Lagoon in that size range had 35 hp Yanmars and when the port sail drive siezed and we dug through documentation on the boat we found 100 hour lower seal life. That isn't somehing you forget 600 miles East of South Carolina.

[django37]

Originally Posted by Auspicious

Maybe. The Lagoon in that size range had 35 hp Yanmars and when the port sail drive siezed and we dug through documentation on the boat we found 100 hour lower seal life. That isn't somehing you forget 600 miles East of South Carolina.

Have a Lagoon 380 with Volvo engines. Volvo says 7 years on the saildrive seals

[Auspicious]

Originally Posted by django37

Have a Lagoon 380 with Volvo engines. Volvo says 7 years on the saildrive seals

The ones I experienced were, as I said, small Yanmars.

It does seem odd to specify seals in years instead of engine hours.

Regardless, seal drive service interval is something that should be considered when contemplating purchase of a boat with sail drives.

[CaptainRivet]

Originally Posted by Auspicious

The ones I experienced were, as I said, small Yanmars.

It does seem odd to specify seals in years instead of engine hours.

Regardless, seal drive service interval is something that should be considered when contemplating purchase of a boat with sail drives.

Lower seal is the one at the propeller and when it fails you get oil into water on the sail drive on the volvo ones. Strangewise I cannot find anything about service life on them in the manuals of my 130S Volvo.
7 years is the diaphragm on sail drives. Like rig an insurance thing, know boats with 16year old diaphragm that still go strong. Look for little cracks in the diaphragm, then change if they show up.

[CaptainRivet]

Diaphragm in years is not odd as the damage occurs due to aging of the rubber material.
There is little till no difference if your boat is on anker, slip or motoring to the life of your diaphragm of the saildrive, that's why its service life is in years.
Lower seal is different, when not motoring its not wearing so its service life is in engine hours.
There are other stuff where both is considered eg oil change which is 200-400h or every year, whatever occurs first.

[Auspicious]

@CaptainRivet - agree. It was the lower shaft seal that failed on the Yanmars (well - the port side one). As you say, salt water got into the drive leg and it seized. Really lovely 600 nm East of South Carolina. *sigh*

Oil changes are less of an issue. Just an inconvenience as that can be changed without a haulout.

[Cadence]

Just don't pick up any monofilament fishing line.