FPB 64-5 Get Home Auxiliary – The Tradeoffs

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We are just back from a quick trip to New Zealand to check on the engine room layout now that a get home system is being added to the FPB 64s. Those of you who have been aboard one of the FPB 64s knows the engine room is a work of art. Circa, our clients, and ourselves are concerned that the hit on engine room access and aesthetics be minimized with this extra diesel.

As you can see from the lead photo the 100 HP Yanmar is very compact. In the context of an empty engine room it looks positively diminutive.

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The Yanmar goes where the Kabola boiler once stood, while the Kabola moves overhead. Access on the outboard (port) side of the little diesel isn’t overly generous, but is still better than the main engines on most yachts, and everything is accessible.

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The Yanmar will be soft mounted, and connected to a remotely mounted v-drive with a CV axle.

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The remote ZF gearbox gives  us a flatter shaft angle for better efficiency while keeping the engine out of the way.

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The plywood box above the Yanmar represents where the Kabola heater will now reside.

This set up looks like it will not materially impact the engine room. But there are some hits on propulsion efficiency, drag from the skeg and disturbed water flow to the main propeller being chief amongst them.

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We’ve previously discussed the full skeg which protects the get home prop. Here are a couple of shots of the finished shape.

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There are two types of drag with this skeg. The first is from the cross sectional area of the skeg. The forward section is fatter than ideal for drag so there is room for the transmission to drop down and improve shaft angle. Then there is wetted surface drag. Between form and wetted surface drag we are easily going to cost ourselves three to four percent in efficiency.

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The other issue is interference with the water flow to the main prop. The get home skeg is well outside the swept main prop area, so we are hopeful the negative here is on the order of a percent or less. There will also be an impact on maneuverability with the second skeg. The FPB 64s  handle so well now, without their bow thrusters, that we can afford to give up a bit of close quarters handling.

Bottom line, we are talking a three to five percent increase in fuel burn for the insurance of the get home system. Worth it? Only our clients can answer that.

Posted by Steve Dashew  (October 22, 2011)

11 Responses to “FPB 64-5 Get Home Auxiliary – The Tradeoffs”

  1. Pete Rossin Says:

    Hi Steve

    What thickness of plate are you using on the get home skeg? I seem to recall other gear outboard of where the Kabola sits that requires access/maintenance. Will that stuff be relocated as well?



  2. Steve Dashew Says:

    Hi Pete:
    The get home prop skeg has similar scantlings to the main prop with both having 10mm (3/8+) side plates. I think we can now conclude that this is hell for stout, would you not agree?

  3. Dan Bennett Says:

    The craftsmanship looks incredible. Still a beautiful boat series.

  4. Chris Says:

    I saw that one or more of the early 64’s are coming in for a get-home retrofit; are their mods to the hull this elaborate, or is there a simplified version for them?
    Either way, another point for unpainted aluminum; hot work is not nearly as big a deal without the paint job to worry about.

  5. Steve Dashew Says:

    Hi Chris:
    Avatar, 64-1, is to be hauled next week to have her Get Home system fitted. It is the same approach as the new builds.

  6. Michael Seng Says:

    Given the efficiency losses and given the bolt on transom’s extra space would there be the possibility of a swing down “Outboard”? Or, is there not enough torque in the largest to swing a prop large enough to make decent head way (does anyone make Diesel versions)? Regarding Circa – they do beautiful work!
    Thanks again for taking the time to “take us with you”!

  7. Steve Dashew Says:

    Hello Michael:
    We have looked at outboards over the years, but have never found a satisfactory solution for other than calm water. The system we now have will make progress on a day you;d rather npt encounter, which makes the efficiency losses worthwhile.

  8. Patrick S Lasswell Says:


    If your day is already bad enough to require an emergency engine, the joys attendant with outboard motor installation would not improve anything and might well get you killed. For example, before you get up to speed you might well be “pooped” by following (for the moment) seas. Unless the outboard’s intake height exceeded the freeboard, you’d have a second dead engine to go with the first.

    Additionally, while Steve bemoans the negative aspects of the skeg on drag, he neglects to mention here the benefit of a propulsion system anchored to the hull of the ship along a large area, reducing the need for heavy bracketing on the extremes of the vessel an outboard motor requires. With vessels of such fine balance as the FPB boats, it is easy to forget that slapping on a couple tons on the transom would be more than unsightly. If you want a demonstration, strap a 3hp outboard onto the the back of a stuffed hiking backpack and go to a party for Halloween dressed as the “ghost of fine engineering defiled.” When the going gets choppy after the forth drink, you’ll better understand Steve’s wisdom…unless that costume is working for you with the ladies.

    Finally, Steve probably only consented to the “get home motor” only after he convinced himself that he could get home from the middle of the emptiest part of the Pacific. He might have put the specification closer to “limping home” to Whangarei from anywhere in the entire world. In all likelihood he’s probably uncomfortable that the Yanmar is only good for a few thousand hours before minor maintenance.

    Personally, I’ve been onboard a high-performance outboard craft when the lower transmission goes in high winds and heavy seas. Sign me up for the sturdy propulsion, please.

  9. Michael Seng Says:

    Steve, Thanks
    Patrick, thank you for the expanded explanation – I will pass on the Halloween costume … I would have capsized long before the 40th drink though!
    Thanks again, to both of you! Have a great holiday!

  10. Douwe Gorter Says:

    Hi Steve, I came across this posting when searching the internet for V drive solutions. I own a new build Dijkstra 55 foot aluminium pilot cutter and we have an issue with the drive which is very noisy. The yard installed a PRM G2000 transmission box which’ bearings in hindsight are not capable to handle the propellor thrust. I may have the change the setup where we will have to replace the G2000 and current (Technodrive) gearbox with a remote V drive. The engine is a 90 BHP Betamarine (2600 rpm).

    I noticed you are using a ZF V drive.

    Could you possibly let me know the type of the ZF V drive and your experience with this particular gearbox?

    Thank you in advance for your help!

    Best regards,

    Douwe Gorter, the Netherlands

  11. Steve Dashew Says:

    We’ve been using the ZF 280 IV transmissions, which I am guessing is a little large for your needs. We have used ten of these V-drives without incident so far, and several pairs of the same transmission in straight configurations.