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Post 43 Deadrise

Discussion in 'Post Yacht' started by Sea Viking, Oct 18, 2023.

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  1. Sea Viking, Oct 18, 2023
    #1
    Sea Viking

    Sea Viking New Member

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    I have a 1984 Post 43 with 671's and was wondering if anyone knows the deadrise angle from just forward of the engines to the transom? I am upgrading the electronics and would like to purchase a transducer prior to hauling out.
  2. Capt Ralph, Oct 18, 2023
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    Welcome to Yacht Forums.

    Thru hull 'ducers have a one piece fairing block that is fitted in the spot available.
    Tilted angle, flush 'ducers only have one or two extra angle options.
    I understand your wanting to pre-order, IMO it may be smarter to wait till up and determine where it will go best, then determine the hull angle at that exact spot.

    I do recommend a real thru hull 'ducer and fit the fairing block accordingly.
    IMO, Those flush 'ducers are not worth a flip at speed.
    Some issues have already been posted here before.
  3. d_meister, Oct 19, 2023
    #3
    d_meister

    d_meister Senior Member

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    You can eyeball the potential locations inside the hull to guesstimate if the inner and outer hull location would be roughly parallel. You could then measure the area with an electronic level device or even a phone app. There's some range in the transducer fitment angles. From Airmar "Chirp" type:

    upload_2023-10-19_9-24-49.png
  4. Greg Page, Oct 19, 2023
    #4
    Greg Page

    Greg Page Active Member

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    My transducer is underneath the port engine. I can measure the angle there (inner, no frames there so should match outer) if you would like. Note I have CAT's, space under a DD may be different. I think it's been in that location before the repower by PO but I can't swear to it.

    You can see it at bottom of the photo. My engines are shorter than the DD so don't judge by the forward mount, mine are further aft. You can see the original mount holes further forward on beam.

    Small 140503.jpg
  5. Capt Ralph, Oct 19, 2023
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    Wow, sweet install. I assume a ZF clutch offering that down angle so well?
  6. Capt Ralph, Oct 19, 2023
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    I see a real 'ducer down there with fairing block. Should be in real clean water mounted there.
  7. Greg Page, Oct 19, 2023
    #7
    Greg Page

    Greg Page Active Member

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    Transmissions are Twin Disk.
  8. Greg Page, Oct 19, 2023
    #8
    Greg Page

    Greg Page Active Member

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    Transducer is happy there. Water pickups for GenSet and on opposite side AC are just in front of the thin bulkead and both run fine underway up to top speed so good water flow for them too.
  9. Capt Ralph, Oct 19, 2023
    #9
    Capt Ralph

    Capt Ralph Senior Member

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    With a down angle or is it the picture that makes the engine look level?
  10. Greg Page, Oct 19, 2023
    #10
    Greg Page

    Greg Page Active Member

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    Drive train is straight. Engine beds are on shaft angle.
  11. Greg Page, Oct 19, 2023
    #11
    Greg Page

    Greg Page Active Member

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    Sorry for the derail

    Not the best photo but gives an idea how the deadrise flattens out from the engines (reference the transducer block) going aft to the transom.

    Transducer 163218.jpg
  12. mapism, Oct 19, 2023
    #12
    mapism

    mapism Senior Member

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    I'm sure it is, but your hull photo suggests it's rather the prop that could be not so happy.
    Such a big transducer right ahead of it is bound to disturb the water flow, to some extent...
  13. Greg Page, Oct 19, 2023
    #13
    Greg Page

    Greg Page Active Member

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    Port engine runs 3% more load at cruise, washes out as hit govenors at full throttle. Engines are same rotation, port transmission runs in reverse. The extra gear set would be expected to add 2-3% efficiency change (yes, I have designed torque split transmissions) so is well within expectations for good design. Wake from transducer would be on shaft centerline, so at the minimum impact to propeller, wake head loss but no swirl (I also design propellers).
  14. Capt Ralph, Oct 19, 2023
    #14
    Capt Ralph

    Capt Ralph Senior Member

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    Just so cool to see an engine with room all around, including under the saloon deck.
    I sure you are a happy owner.

    Sorry to keep de-railing this thread.

    At first look you would think some disturbance at the prop, That far forward, I don't think so.
  15. Sea Viking, Oct 20, 2023
    #15
    Sea Viking

    Sea Viking New Member

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    I appreciate the info. Planning on diving the boat this week or the next to replace the zincs before the winter and will take a inclinometer to hopefully measure the deadrise. As Capt Ralph suggested I’m going to look into a fairing type transducer opposed to a flush mount. If I cannot get a clear picture of the angle I’ll wait until haul out.
  16. Greg Page, Oct 20, 2023
    #16
    Greg Page

    Greg Page Active Member

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    If diving: nail a string with a weight tied to the other end to a piece of board. Put board edge on the bottom and scribe the board where the string crosses. Can get what angle it is when surface.
  17. boatpoor, Oct 20, 2023
    #17
    boatpoor

    boatpoor Active Member

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    You should be able to use a degree level or angle finder to determine the deadrise at a particular spot in the hull from the inside with the boat floating at rest. I went through the same exercise last year on a 1993 46' and it's 12.5 degrees just ahead of the pickups for the generator and AC. As Greg' photo suggests, the hull flattens considerably from there as you move astern. More so on the older hulls than the later models.
  18. Capt Ralph, Oct 20, 2023
    #18
    Capt Ralph

    Capt Ralph Senior Member

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    I would still suggest; Not to cut that fair block till you have the best spot selected, then you can exact form/fit to that location.
  19. Greg Page, Oct 21, 2023
    #19
    Greg Page

    Greg Page Active Member

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    By coincidence (or design) the 43 II deadrise at the bulkhead between the engines and the GenSet/AC water pickups is also 12.5 degrees. Happened to be in the engine room this morning.
  20. Sea Viking, Oct 31, 2023
    #20
    Sea Viking

    Sea Viking New Member

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    Update on the deadrise, I was finally able to get in the water and check. As Greg suggested, I used a small 2x4, short steel leader, and a 10 ounce ball weight to make up an angle finder with 10 and 20 degree marks. Picked a very smooth day and no one on the boat. I was able to let go of the wood and let it rest without touching it against the hull. There is a fairing block style transducer forward of the port engine and aft of the generator pickup that measured 8 degrees. Aft of the engine where there is a flush mount transducer measured 7 degrees.
    Greg Page likes this.
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