Panga 25 With Bracket

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Crystal Craft
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Re: Panga 25 With Bracket

Post by Crystal Craft »

Tom W and others thank you!
Tom W my 2 batteries are in the consul under the forward facing seat. Can easily move it all forward 6 in as needed. In addition I’m planning on my fuel tank near the bow details on exact size and location tbd but up front. This could move me closer to what your calculations suggest. And also my setback is 18 in not 24 and the kicker is 15 back. Both adjustments should temper my need to move more forward. It think. Does my thinking wash with your figuring? Thank you!!
Photo my consul type on another build 2 batteries under forward seat plan on same on Panga 25
Steve
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TomTom
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Re: Panga 25 With Bracket

Post by TomTom »

The problem with using fuel further fwds to balance the boat is it changes as you use it up.

If you can it is better to move fixed objects - like the whole console with fuel under it and try and keep the fuel close to the Center of gravity

Chessie
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Re: Panga 25 With Bracket

Post by Chessie »

Thanks everybody, good stuff and it seems as though this leaning more towards a bracket is acceptable WHEN DONE CORRECTLY.

TomTom
Were you saying full width cut out or full height transom with bracket. Don’t need full twins, just the single and a kicker.

TomW1
I followed most of what you said but the exact calculations lost me a little.

It seems that weight x 10 on the rear gives you total leverage and offsetting that is weight x distance shift from original placement? Somewhere in there is an adjustment adjustment for difference in motor location.

I’m think I can make up 200-300# with foam in a bracket plus extra in hull. I will foam the entire underside for the “unsinkable” version.

Crystal Craft
I followed the concept and have seen reinforced stringers and knees on rebuilds but not sure how to develop the actual design. Did you get your changes from somebody?

Fallguy
Everything you said is what I thought and therefore if I can mostly overcome the squat at rest, I’m OK.

I’ve seen that picture and it is one of the ones that made me ask. Also, I will be 200# lighter than that due to weight difference in a 90 HP or a 9.9.

That Angler Panga is only 2” wider on the beam than the PG25 and I believe 1’5” longer but a fair amount heavier. It also looks like the Angler carries the width to the transom where the PG25 narrows a bit.

Chris
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TomW1
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Re: Panga 25 With Bracket

Post by TomW1 »

Chessie foam in the bracket does not count as brackets are out of the water when on plane. Any Armstrong or SS you purchase will be this way. They do support the weight of the motor at rest. If you are having a bracket built there is no need to add to your drag by having it in the water when on plane.

As far as my COG weight calculations are concerned they are simple, for every 1lb added 10ft behind the COG you must add 10lbs forward of the COG. You can do 2lbs 5ft or any combination. COG being longitudinal center of gravity. Jacques normally places this a little bit behind the console, say where you stand. So for the calculation for new things add the new weight * the length from the COG and that is the weight that must be moved forward in some type. For older things like the motor it is just how far they are moved back times there weight. Does that make sense? If you have any questions let me know.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Chessie
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Re: Panga 25 With Bracket

Post by Chessie »

Thanks Tom, that makes it perfectly clear and something to work with. I’ve read some of the comments about the console location and I believe the online study plans even mention it with respect to balance.

My foam thoughts were only to combat resting displacement, understanding it’s not an issue while on plane.

Chris
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Crystal Craft
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Re: Panga 25 With Bracket

Post by Crystal Craft »

Motor weight on bracket? In the plans the 25 Panga is rated for 75 o 125 hp...that could put a 400 lb motor on the transom. So my 60 Tohatsu at 238 lbs, even 18 inches back should not amount to any big deal to make COG adjustments. Plus even the 63 lb trolling motor is still "less"..... If my motor choice was bigger I can see the need to look at this more seriously. Realizing the boat is designed for a much bigger and heavier motor on the transom directly...don't you think I'm ok...to just keep my 2 batteries in the console and my tank forward? Your thoughts appreciated. Today I'm doing the transom knees...copy photos when I have something to show...
Thanks!
Steve
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fallguy1000
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Re: Panga 25 With Bracket

Post by fallguy1000 »

So, usually a designer can spec cog under a set of givens.

You change those givens by a certain amount and the result is measured in kgm or ftlbs.

For example, a move of the engine 2' back and an engine 100# heavier is a moment of 200 ftlbs aft,

The bracket at say 50 pounds is a moment of 50#x1ft averafe aft.

You'd end up with a 250 foot pound moment roughly.

If the fuel tank is 50 gallons or say 325# and the operator is 200 and the console and seat is 100, then if you consider the tank half full on average; you'd have 175 pounds of tank n fuel and 300 pounds of crew and seat and console or a total of 475 pounds. Moving them 6" forward results in a 237.5 foot pound moment forward. Most likely the 6" number will get you close, but you can be more precise.

The result of my example is the cog was moved by 13.5 foot pounds aft.

A double bench and batteries and more stuff under the console might mean a 4" move forward.
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Chessie
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Re: Panga 25 With Bracket

Post by Chessie »

Tom, Fallguy

I understand the initial leverage calculation but am trying to make sure I understand the adjustment calculations.

The adjustment calculation is based on the weight of the object being moved X the distance being moved. IT IS NOT required that the move be forward of LCG. It also requires assumed original weight of object and position of said equipment.

A console adjustment is based on its original designed location which is different from designed assumption of stern mounted batteries.

For example

In the stern, a 100# battery moved forward 5’, offsets 500# of leverage but a forward move of 10’ offsets 1000#, 15’ 1500# and so on.

Potentially none of these moves would be forward of LCG.

At approx. LCG, 500# of console and crew shifted forward .5’ offsets 250# but a 1’ shift would offset 500#, and moving 1.5’ forward offsets 750#.

Is my head straight yet?

In theory, how would ballast be calculated, such as 50# of lead. Would it be calculated from transom or from initial LCG?

Chris
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fallguy1000
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Re: Panga 25 With Bracket

Post by fallguy1000 »

Sorry, no, you cannot simply add weight to the stern without countering it on the other side of center of gravity. The center of gravity is dynamic.

If you take the center of gravity of a boat and let's make the following example.

25' boat
CoG is 11.5 feet from transom at dwl.
Mass of boat is 3000#

Moving the batteries of 100# designed for 10' from cog up 5 feet reduces that lever moment by 500 ftlbs. The center of gravity then moves forward, but if you never seesaw over the center of gravity; all you are doing is shifting the cog. If you do nothing else; in order to balance the seesaw; you would be moving the center of gravity forward. How much? Well, that depends on the vessel size. Here 3000.

The new cog is as follows:

500 ftlbs/3000lbs = 1/6 foot or 2" move of the cog forwardp

The only way to stop this phenomena is to place weights on the other side of cog or to move weights on the other side of cog. Otherwise you are only moving the boat's center of gravity. Now some boats are more tolerant of that than others. This subject is for the designer really to discuss his boats ability to adapt to weight changes and effects.

Hope this helps.

Dan
Last edited by fallguy1000 on Sun Jan 17, 2021 2:20 pm, edited 1 time in total.
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fallguy1000
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Re: Panga 25 With Bracket

Post by fallguy1000 »

Sorry, I got on my bike and got all confused if I did it right. My original post is right. If all you do is move aft things forward, but not beyond center of gravity, all you are doing is moving the center of gravity.

The center of gravity moves forward when weights move forward. But you want the cog to remain close to spec or as tolerated by the vessel.

Sometimes a drawing is best. Maybe I will draw something later today.
My boat build is here -------->

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