Is my boat sitting too low in the back?

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 9:37am
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Titanium
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I would have the hussler , gross weight on water.. incuding ppl, guestimate 1100/ 1150

Do you know your WoT speed, on flat water at best trim for that speed?  and is the rpms close or within the manufactures max rpm range?

If so the gross weight cdan be calculated reasonable close.

Or do this with tape measure and kitchen scales.
You have to do the measurements real accurate.
 If duel axle, remove 1 set wheels, the remaining set the trailer still sits reasonable well.
Just got to find the doc wrote out few yrs back.

"Did you know you can weight the boat (only the boat)  on the trailer with bathroom scales?

 keep the engine tilt as low was possible, but high enough to just clear the ground..

 measure all weights in lbs

 measure All distances in inches

1/Put the sales under the hitch, a length timber long enough to JUST lift the hitch and take the weight on the scales...  with trailer level or slightly low at the front.

record the weight  call it   w1

2/ slide the boat back on the trailer about 12" to 20"

 measure the distance accruately and record it  d1.. the accuracy of this measurement is very critical to the end result

 d1

3/ now with hitch same height record the weight as before You may not be able to move the boat a full 20" as the balance on the trailer may put the hitch up in the air....if so just move back till just have enough weight to measure at the hitch....OR put a known weight on the bow deck.. say a 40L water container full right at the start , before taking 1st weight (W1)

OR simply move a lot of stowed gear equipment well forward.

Measure this weight    w2

4/ now measure the distance from the center  where the bit of wood its on the scales to the center of the axle.

d2

 Boat weight = d2(w1-w2)/d1

If put an extra weight on the bow of the boat, now subtract that weight.

Sounds strange.. like stuff like center gravity, weight of trailer etc... If one does the full calculation create the full equation, including these constants and gravity , center of mass and stuff....then compact the equation, all those factors cancel out and one is left with the above equation. Therefore if the constants like trailer weight... which we dont know cancel themselves out then we dont need that information in the 1st place"


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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 10:06am
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You could just slip the boat off the trailer onto the back lawn and take the trailer down and weigh it with out the boat on.
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Post Options Post Options   Likes (0) Likes(0)   Quote Sambo Black Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 11:18am
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Wow that’s quite the equation there steps but very clever I must say

I think that I’ll slip the boat off the trailer if I need to but can’t do that at the moment as I’m in the process of moving house so the boat is in storage right now. I’m a few weeks away from getting into the new house.

As stated earlier though, there is a name plate on the trailer stating 260kg and I confirmed that when I spoke to the manufacturer over the phone. Just had to add on spare wheel for my calculations.


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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 12:24pm
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I think I found the doc:
  • echnique to weigh small boats
    Thank you for remembering me, Steven. Yes, the 'Lathrop Method' is the weighing procedure I posted some years ago. I have used it to weigh boats up to 7000 lbs - the thing with heavier boats is to find a scale that will handle the tongue weight, which in the instance of the 7000 lb boat was around 400 lbs. For a boat of around 1000 - 1500 lbs, an ordinary bathroom scale should suffice. To reiterate the "Lathrop Method':

    Weighing a boat on a trailer


    Shift the boat as far forward on the trailer as it will go.

    Place a scale under the tongue support leg. Record the weight.

    Measure the distance from the tongue support leg to the tip of the boat bow. Record this.

    Shift the boat aft on the trailer a couple of feet, but not so far as to allow the trailer to tip backwards.

    Place a scale under the tongue support leg. Record the weight.

    Measure the distance from the tongue support leg to the tip of the boat bow. Record this.

    Measure the distance from the tongue support leg to the centre of the trailer axle (if a twin-axle trailer, measure to the point exactly half-way between the axles). Record this.

    Calculate the boat weight using the following formula:

    W = C(W1-W2)/X

    Where:
    W = weight of boat
    C = distance between tongue support leg and centre of trailer axle(s)
    W1 = first (heavier) scale reading
    W2 = second (lighter) scale reading
    ` X = distance boat was shifted between scale readings
  • 03-17-2016, 12:30 PM
    Tom Lathrop
    Re: Technique to weigh small boats
    I had heard about this method of weighing boats much heavier than the available scale but was not able to find it when needed so in the 1990's I did derive the formula shown on Ray Macke's site. I use it several times during construction of a new boat with blocks under the chines so the final weight can be projected fairly accurately. A by product is also a good CG estimate. I find this method to be accurate up to at least 3,000 pounds which is as high as I've used it.. Problem with larger boats is mainly that they will normally sit on dual axle trailers which the method does not work fo
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 12:25pm
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That looks similar to your method Steps so I'm guessing thats a pretty good way to do it
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Post Options Post Options   Likes (0) Likes(0)   Quote Sambo Black Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 1:16pm
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I must say I’m intrigued to find out how accurate that is.

I may give it a crack
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 1:28pm
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I think you will find it's a pretty accurate method it looks like both Steps and that stuff I posted up are saying the same thing
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 2:35pm
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Originally posted by smudge smudge wrote:

I think you will find it's a pretty accurate method it looks like both Steps and that stuff I posted up are saying the same thing
LOL
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 4:39pm
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Wow that’s quite the equation there steps but very clever I must say..

 Keep in mind this is basic 1960s high school UE maths..

 I didnt work it out.. Back when was at school  UE yr we had a physics teacher (Sciences where split at SC level back then) and he came out with it, not for the maths bit but to illustrate vectors , force etc in practical terms.
 We have sed it to weigh small diggers, a bob cat, couple vintage cars, few other things over the decades.

 Accurate? The greater the distances used, and the smaller the units of distance and mass, used the more accurate it becomes.
 Its like batching in a lab.. say your batch is 100gms and measure +/- 1 gm  (1%)
Then take that same batch and increase to say 1,000kg in the factory and  measure to =/- 5g thats 0.0005% error.. think got the right number zeros in my head Cool

 I have posted this up quite a few times over the yrs.

 Edit:
Now this part I have not heard of before , for duel axles..
Which is why I suggest and we have removed a pair of wheels on duel axle.'

Measure the distance from the tongue support leg to the centre of the trailer axle (if a twin-axle trailer, measure to the point exactly half-way between the axles). Record this.

 I could be wrong here, boats and loads dont sit on duel axle trailers with even weigh on both axles....which may make that not work????
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2022 at 5:06pm
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Damn this got me curious being called the "Lathrop Method"
 Never head of it... only practical application have come across was weighting small competition boats yrs ago.

So just done a bit of digging came across this by lathrop..
Tom Lathrop
09-02-2018, 07:56 AM
The method in #14 seems to be doing well

I cannot take credit for originating this method Clinton. I had heard of it previously but could not find the source when I needed to take some successive weights during a building process in order to predict the final weight of a new boat design............... I just made some calculations based on seldom used college statics to regenerate the formula.

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Post Options Post Options   Likes (0) Likes(0)   Quote kimber7wsm Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2022 at 6:50am
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If the dual axle used an Equalizer between the axles, would that not mean the load becomes centred on the equalizer bolt? If so then would work for dual axle.

The equalizer becomes the pivot point, so to me it should work.

Not sure if it would work with a non-equalized dual axle set though.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 12 Feb 2022 at 8:36am
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That was sort of my thinking as well, but not sure that centered means 1/2 way between the axles ....actual equal load on each wheel...
So it sort of 'thinking that' and missing something, rather than 'knowing'

 Which is why I mention removing a set wheels from the old high school project example.
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