FPB 78 Series – Furniture Construction and the Weight/Center of Gravity Game

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Speed is a critical component of long distance cruising, as is a structure that carries a high factor of safety. We also want lots of heeled stability and the ability to recover from a capsize. But there is a conflict between these elements, and it revolves around weight and center of gravity. 

The FPB 78s will cruise at 11+ knots several times across the Atlantic before needing a fuel stop. They also have the highest factors of safety of any of the yachts we have done to date. The fuel payload is heavy, as is the structure, so we need to save weight elsewhere to compensate. Cue the interior.

With the FPB 78 Series we are switching to a performance sailing yacht style of interior construction. Head and hull liner panels, furniture modules, and the grounds to which these attach have been put on a diet. The result is a savings of weight and lowering of the vertical center of gravity, both critical to accomplishing our performance goals for the FPB 78s.

The Great Room settee carcass above is a case in point. Panels have lightening holes (which also helps with ventilation), and the other furniture/cabin sole/coaming to which this is attached provides strength. More care in building and installation is required, increasing cost, but the weight savings throughout add up.

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Here is another example, the centerline furniture module between the guest cabins aft. Until installed this unit is unstable, so a temporary end panel is used to maintain shape. Once secured in place, the bulkheads to which module is attached stiffen the unit.

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With the FPB 78 Series we are going back to foam cored doors. These have not been necessary until now, although we used them on many of our sailing yachts in the past. The weight savings from this are not huge, but this is one small piece of a large effort.


The biggest savings with the highest VCG impact are in the headliner panels. The headliner panels and the grounds system to which they attach have been put on a serious diet, resulting in a 50% reduction in weight. The panels are harder to fabricate and one must take care during installation and removal.

The result of all of this fussing around is a two percent reduction in overall displacement at cruising payload, with a lowering of the VCG by a couple of percent as well,  Not much, you are probably thinking.

Here is where it gets interesting. By trading this interior savings for a heavier hull bottom we end up at the same displacement, but since that weight we added back is low in the boat the VCG drops . With the lower VCG we can now reduce lead ballast, and this is a big number. This in turn allows for a larger battery bank (low), heavier propulsion package (also low), and thicker (heavier) insulation.

The end result is a quieter boat (engines and insulation), safer structure (heavier bottom plate), better cruising range and faster ocean crossing speeds (more efficient propulsion package).

All of which stems from putting the interior on a diet.

Posted by Steve Dashew  (February 26, 2015)

10 Responses to “FPB 78 Series – Furniture Construction and the Weight/Center of Gravity Game”

  1. RobS Says:

    If system weight savings are of interest then have the lithium ion battery offerings to replace the
    large lead acid traction batteries reached your reliability requirements yet?

  2. Steve Dashew Says:

    Howdy Rob:
    LI bateries are too fussy for our taste, and weight down low is OK in any event.

  3. Jack Salisbury Says:

    Thanks for keeping us up on the structure of the boat. Much appreciated

  4. Dan Hoban Says:

    If you are trying to save on weight why aren’t you using honeycomb with wood veneer laminate for the cabinetry, flooring, and headliner?

  5. Steve Dashew Says:

    Hi Dan:
    Where and how to save weight and the cost/performance/endurance equation is at the heart of our decision making process. Honeycomb, which we have used on a few projects, tends to be more expensive, more fragile, with less noise attentuation properties, than foam cores. And the weight difference is not great. The preceding on the assumption that transfering shear loads between skins is not a critical requirement. In terms of the headliner panels, there would be an increase in weight. Cabin soles for the great room require too much flexibility for hard spots to attach furniture. The lower deck sole is well below the VCG. Lowerdeck bulkheads might be a area where honeycomb would make sense except we need the plywood skins for noise abatement.

  6. John Thomson Says:

    I worked in the Marine Electronics industry for over 20 years. I had my fill of Tupperware Monsters, Wind Horse was a breath of fresh air.

    Over the years of retrofits, the fragility of overhead panels, combined with construction methods that ignore the fact that equipment gets replaced over the life of the boat, have made life very difficult at times.It can be a vexing problem to combine aesthetics with function. I have seen 4 X 8 sheets of 3/4″ plywood, Asbestos, fabric covered foam on a wood frame, all the way down to office grade dropped ceiling panels. While hideous, the dropped ceiling was nice to run the 1″ armored satcom cable over/through. Have you addressed this issue so that although light in construction, the panels are rigid enough to come down in one piece for inspection or upgrade?

  7. Steve Dashew Says:

    We like to have access to EVERYTHING onboard, John:
    Hull liners, outboard of shower modules, and above the headliner panels. Headliner panels are held in place with hidden “Fastmount” hardware. Removal of the headliner panels which are this light takes more care than if they were heavier, but it is nothing extraordinary.The headliner panels on the FPB protype Wind Horse were about the same weight, and we had these in and out over the years without a problem.

  8. Shannon Says:

    This is the kind of attention to detail that impresses me to no end. On a big boat like this there are thousands of little details. Any one of which isn’t a big deal but, like you say, the little details add up to something extraordinary. That’s where many designers drop the ball. They view to many little details as not a big deal & they add up to something average.
    Attention to detail is telling on anything from a house to a car to a yacht. If the designers or builders don’t put effort into the details it’s a pretty safe bet that they don’t put much more effort into the big things either.

  9. Peter Bateman Says:

    Whilst you are looking at your traction batteries, I would suggest that you have a look at Lead Crystal. This is a piece of very disruptive technology, Better performance than Traction less maintenance issues and greater cycle life and altogether better than Li Ion in your solar setup.
    We are running these on a 35 Kw 3 phase solar installation and are very happy.

  10. Steve Dashew Says:

    Thanks Peter:
    Specfics on suppliers you have been happy with, etc. would be appreciated.