Doing the math

While in Savannah we finally accomplished something we should have done a long time ago–we measured our mast. When we bought the boat it was advertised as being “ICW friendly”, although the boat had never been in US waters and thus had never actually travelled down the ICW.  The rule for the Intracoastal Waterway is that all fixed bridges are supposed to be 65 feet above the water at Mean High Water, unless otherwise marked.

 

Mean High Water (MHW) is the average of all the high water heights observed over a period of several years. For example, in the USA this period spans 19 years and is referred to as the National Tidal Datum Epoch.

Here’s the info that came with our boat:

DIMENSIONS & DETAILS•  Flagged:  USA •  VAT:  Paid (France) •  Builder:  Alliaura Marine •  Designer:  Marc Lombard •  Model:  435 •  Owner’s Version •  Year:  Model Year 2000 (manufactured 1999) •  Construction:  GRP-foam sandwich construction  throughout with resin, multi-axial glass and PVC foam.  Extensive use of vacuum infusion to improve structural efficiency and reduce weight.  Bureau Veritas certification. •  LOA:  44′ 2″/13.45m •  LWL: 42′ 2″/12.85m, •  Beam: 23′ 2″/7.06m •  Draft: 4′ 5″/1.35m •  Bridge Deck Clearance:  2′ 6″/0.76m •  Displacement (empty): 9043 kg/8.9 tons •  Displacement (max): 12,193 kg/12 tons •  Fuel: 200 gallons •  Water: 200 gallons •  Mast height: 58′ 6″‘/17.84m •  Bridge clearance:  60’/18.29m •  Headroom:  6′ 6″/1.98m •  Hull material:  Fiberglass

58’6″… we should be fine, right? But then we noticed while staying in the Brunswick marina that our mast looked as tall as the mast of the Leopard Catamaran next to us. The owner of that boat said he had a 66 foot clearance. Uh-oh. So we got out the level and measured from the bottom of the mast to the waterline= 7 feet.  58.6 + 7 feet + instruments on top of mast > 65 feet.  It seemed the ICW was a no-go.

Hitting a fixed bridge will dismast a boat.  And this isn’t an option for us:

So we went “on the outside” from Brunswick to Savannah (that is boat talk for going out in the Ocean as opposed to up the ICW aka “the ditch” which is the waterway between the mainland and barrier islands).

While in Savannah we decided to revisit the situation. The fixed bridge next to the marina said it was 74 feet tall at low tide. Georgia easily has 9 foot tides, maybe if we knew our mast clearance for sure we could go under some of the bridges at low tide? We wouldn’t be as depended on the weather to travel and for our return trip South would not have to fight a 2 knot Northern Current in the ocean.

Ben and I (mostly Ben) hoisted Kim up the mast in a Bosun’s chair. Here is her view from the top:

She took a rope with her, put a knot in at the top of the mast and the top of the first fixed instrument, and I put a knot in the rope at the bottom of the mast. When we got down we measured the rope, and used a laser level to remeasure the distance from the bottom of the mast to the water level.

Distance from water level to bottom of mast= 7 feet
Distance from bottom to top of mast= 52 feet
Distance from top of mast to instrument= 16 inches
+ flexible VHF antennae about 2 more feet

= about 63 feet.

We were too hot to actually do a happy dance on the trampolines, but we were dancing on the inside.

The next day we started going under bridges.  But let me tell you, even at low tide it looks close.  So far our procedure has been to come to a complete stop as we approach the bridge with one person looking for the VHF antenna to start bending and the one at the helm ready to reverse.   What I really need is 2 baby aspirin and  a vial of nitroglycerin available to me at the helm because it still gives me a heart attack to watch.  Look how close this appears to be:

 

I still prefer the Bascule bridges:

Northward we go by way of the ditch!!