FPB 97 Performance – What Is Your Guess?

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We will shortly begin a wicked set of sea trials with FPB 97-1. Along with the usual wringing out of the boat before handover, one of the objectives is to gather a data set with which to refine our velocity prediction algorithms.

Predicting performance is notoriously difficult. In our case it’s harder than most, as there is no historical data to use other than our own. Various code packages are mixed with tank, real world, and large scale model test sets to conjure projections.

Propeller efficiency, wake fraction, buttock shapes and flow diversion, engine power curves, trim, even water depth, salinity, and temperature are involved, not to mention fore and aft prismatic, block, and volumetric center numbers. A wicked brew for sure, and to get close requires a healthy dose of skepticism and gut feel. That said, we have to make predictions in order to specify the initial set of props.

What we expect is a closely guarded secret. Nobody has the magic numbers outside of a couple of folks with “need to know”. But we thought you might enjoy speculating. Here are the ingredients:

  • A pair of 300HP John Deere 6068 SFM50 diesels turning 2600 RPM
  • 2.55/1 ZF reduction gear
  • 32.7 m/106′ waterline

Astute observers will note missing data such as prop size and pitch, vessel displacement, and a host of other characteristics. You didn’t want this too easy, did you?

FPB 97-1 has a set of new-to-us Veem (Australia) propellers. The decision to give these propellers a whirl (pun intended) with the FPB 97 is based on the theoretical advantages offered by easily changed “Interceptor” strips on the propeller blade trailing edges. By varying the thickness of these strips, the pitch characteristics can be easily altered. We have been told a diver can quickly change the strips, which would be a huge benefit to all concerned during the sea trial process. And Veem claims some impressive efficiency numbers.

So here is the contest: Initial trials will be done in light trim, with 10 metric tons of fuel and water aboard. They will be in deep water (salt), and in smooth conditions.

  • What do you predict for max continuous cruise speed, defined as 80% of available power?
  • Next, what is your prognosis for wide open throttle?
  • Finally, what do you project the engine load %, fuel burn, and RPM, to be at 11.5 knots?

The winner gets the accolades of SetSailors everywhere, and a cool (yet to be taken) most wicked photograph of FPB 97-1.

Before we all get carried away with the “science” of performance prediction, a cautionary tale: There is a large heaping of BS associated with all things yachting, and none more so than the propeller end of the business. If you stick with the tried and true, the projected outcome has a higher chance of being in the ballpark with the estimates. Use something new and you might get a breakthrough or the opposite. Nothing ventured, nothing gained. When we started the FPB project many years ago with Wind Horse, we took a chance on some very expensive, theoretically highly efficient props from Henleys in New Zealand. We gave Henleys our drag and power train data and they suggested a set of five bladed wheels. The performance of the FPB prototype, while impressive, left something on the table. Henleys, saying their props were perfect, were uninterested in looking further. When Wind Horse found herself back in the States we replaced the Henleys with a set of Michigan wheels costing a third of the originals, and picked up the missing performance in the process.

The Henleys props are now a sculpture on top of our mailbox, the subject of some discourse in the neighborhood. And for us, a reminder every time we drive in or out, to take everything one hears in this business with a grain of salt.

Send us your prognosis, and may the best estimator win!

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Posted by Steve Dashew  (November 22, 2014)

19 Responses to “FPB 97 Performance – What Is Your Guess?”

  1. really? Says:

    A large heaping of BS, indeed. Interested in seeing more actual info.

  2. Markus Says:

    Here is my guess: 14.6 knots @ max continuous power (80%); 15.65 knots @ wide open throttle; 32% engine load – 25 liters per hour (6.5 US gallons per hour) fuel burn – 1’575 RPM at 11.5 knots

  3. Shannon Says:

    Max cruise speed at 80% power will be 12.2 (I am expecting great things from that extra waterline length)
    Full power top speed will be 13.8
    load % at 11.5 will be 71%
    Fuel burn at 11.5 will be 10.3 gallons/hr
    RPM at 11.5 will be 1,750
    Good day guys!!

  4. Bill Says:

    12.2 knot cruise is my guess also.

  5. Shannon Says:

    I spent a long time thinking about it. I think I got the speeds, fuel & RPM fairly close but I think I drastically overestimated engine load at 11.5. I said 71% but I think it will actually be just below 40%. Maybe around 38%. I wasn’t thinking when I said 71%
    We will see.

  6. Johan Says:

    Max speed 24 knots
    Continuous speed at 80% power, 18 knots
    fuel burn at 11,5 knots 5 liter per hour

    This is my quess, wen I compare with yachts with a Fast Displacement Hull.


  7. Scott Evangelista Says:

    Once you dial it in I will give you a WAG mind you not a SWAG of
    Max cruise at 80% of 14.2
    Max speed of 16.1
    Fuel burn at 11.5 of 10.1 gal/ hour

  8. Marcus Nasholm Says:

    Congratulations on a great design.

    Lets start up wit the guesstimates,

    Max cruise speed at 80% of rated power: 13.4kn
    Max speed at 100% power: 14.3kn
    Engine RPM at 11.5kn: 1850
    Engine load 11.5kn: 36% (76kw)each or 156kw total
    Fuel consumption at 11.5kn: 41.5 l/h total or 20.75 l/h per engine

  9. Johan Says:

    Sorry Fuel consumption was nonsense
    I think 5l per Nautic Mile, thus 57,5 liter per hour.

  10. Jim Patrick Says:

    Looks great – Good luck with the sea trials.
    max speed – 80% power – 13.9 kts
    Max speed wide open – 14.2 kts
    Engine loading at 11.5 knots – 71%
    RPM at 11.5 knots – 2100
    Fuel burn at 11.5 knots – 9.5 gallons per hour.

  11. Chris L. Says:

    Max. cruise speed, continuous/80%: 12.3kn.
    Max. speed 100%: 14.0kn.
    @ 11.5kn Load: 74%, 13.2 gal/h, 1920RPM

  12. Steve B Says:

    I just wanna be on the matrix deck the first time it hits warp-speed!

  13. Kerris Says:

    80% load 13.9 knots, full throttle 15.1 knots, 11.5 knots at 1600 rpm with 32% engine load and 36 litres/hour total consumption.

  14. Matt L Says:

    There are some amazingly optimistic guesses so far and a few that are likely to be a extremely close. Instead of venturing a guess, I am going to just enjoy this cone vicariously….in spirit…with Steve B on the Matrix deck.

  15. Ken Kiddie Says:

    My Guess for 80%load 480hp is 14 knots. Top speed 14.9 knots. 11.5 knots should be about 25% load with fuel burn 25 l/h not including ancillaries. rpm about 1100. I guessed 90 tons. The real figures will be very interesting.

  16. Gene LeBeau Says:

    Wide open speed will be 15.5kn; Max continuous at 80% will be 12.25kn; engine load at 11.5kn will be 70% at 1700 rpm with a fuel burn of 8.8gal/hr.

  17. Antonio Carvalho Says:

    I guess 80% load 13.5 kts, full throttle 14.9 kts, 11.3 kts at 1600rpm and 33 lts/hour consumption

  18. Stu Rowe Says:

    I’m Guessing:
    21.5Knot WOT
    18.0Knot 80%
    11.5Knots @1450RPM 20L/PH combined

  19. mike uybadin Says:

    Hi Steve.

    my guess if godspeed can surf 27kts then by 600 hp total, wot 18 kts.

    i was on godspeed when it was in fortlauderdale i loved it. wanted to buy it, it was close, to bad my business contracts cancelled i had to take a step back.

    to the quiz:

    80% power 15 kts.

    %55 fuel 16l per engine per hr rpm 1560 will be 11.5 kts

    lets go with this engine :

    how about yanmar 6 cxvm – gt

    at 856 kg, 509 mhp 374 kw for a top speed of 22 kts.

    for 80 kg more per engine you get 200 hp each total 400 hp not a small figure

    i would be excited if you can beat the so called fat luxury yachts burning burning 5 times as much fuel for the same speed.

    my best for you and family

    mike uybadin fortlauderdae fl.