Heavy Back end!!!

[gazza2006au]

I have no idea where the extra weight has come from if the engine that came off the boat went back on it

[Ronje1]

I think EdBerg was onto something.

Its not necessarily the effect of extra weight.

The see-saw analogy was a good one. equal weights both sides of fulcrum so plank is balanced.

Put just 1 kg extra on one side at the end and that side goes down.

put 1 kg on other side (but only halfway along) and the original side still stays down.

say saw is 10 ft long (5 either side of support (fulcrum).

Put 5 lbs on one end (5 ft from centre). 5lbs x 5 ft = 25 ft pounds.

There's then 5 lbs @ 5 ft that needs to be balanced = 25 ft lbs.

How much would you need to put at 5 ft on the other end? 25 = 5 x ? = 5lbs. Easy as.

What if you only had a lump counter-weight of 10 lbs and you put that @ 5ft. How many ft lbs then? = 10lbs x 5 ft = 50 ft lbs. Would seesaw balance? Nope.

So where would u need to put the 10 lbs to counter the imblance (get 25 ft lbs). 10 x ? =25 ft lbs.

Answer is 2.5 ft from centre to counter balance.

My input is that there needs to be weight forward of the old balance point (wherever that was ). If 2 batteries are not enough to do the job (providing they go well forward), then there's a lot of extra weight gone into the transom than being estimated.

Its a lever and turning moment problem.

https://www.grc.nasa.gov/www/k-12/Wi...of_forces.html

[Noelm]

A boat doesn't behave like a seesaw, there is not fixed, solid pivot point/fulcrum, the back of the boat goes down (say) 5", the front doesn't come up 5", that's why just adding weight to the bow does not counter act a heavy motor on the stern as much as you think, you need to move weight, not just add weight.

[blacklab]

ppppppppppppp

[Noelm]

Yep, been there and done that, helped lots of people to get the best trim possible by moving "stuff" when I first got my old Rebel Cat the anchor well in the front deck was full of concrete, it didn't help level the trim one bit, it took me ages to drill and grind it all out, I ended up moving the batteries up forward a bit and it made a heap of difference

[blacklab]

pppppppppppp

[Lovey80]

From what I understand Blacklab, it largely depends on the shape and symmetry of the hulls with cats. Many do not like too much weight on the arse end.

[Noelm]

The old cat had big heavy engines on it, and the previous owner tried to level it out, which in a way it did, but, only by lowering the bow, not raising the stern (like a seesaw), it made the boat very flighty in a following sea because of the weight right at the front, removing the concrete made the boat entirely different and handling was perfect.

[Ronje1]

A boat doesn't behave like a seesaw, there is not fixed, solid pivot point/fulcrum, the back of the boat goes down (say) 5", the front doesn't come up 5", that's why just adding weight to the bow does not counter act a heavy motor on the stern as much as you think, you need to move weight, not just add weight.

I tried to keep it simple by using the seesaw analogy.

There are 2 separate forces acting on the vessel and they both act vertically. Gravity acts downward and buoyancy acts upward.

Gravity is simply the weight of the boat and the centre of gravity (CG) determines where the balance point is.

Buoyancy is simply the volume of water displaced by the hull shape acting upwards (CB).

If the CG and the CB are in the same place vertically, the hull will sit level in the water.

However, if they're not then they will be creating what's called a "turning moment" (not a moment in time). U could call it a "turning movement/effect".

That will cause the vessel to NOT sit level in the water. It'll either sit bum down or bum up.

Putting extra weight on the stern shifts the CG towards the stern. It doesn't much affect the centre of buoyancy as there's no real change in shape of the hull.

As we've increased the "turning moment" by moving the CG back, then the stern will sit bum down.

We might be able to move the CG back towards where it was originally by "changing the boat's furniture around". Re-distribute the moveable heavy objects by moving them forward ("drag" the CG back towards where it was originally).

However, that will do bugger-all in respect of the CB 'cos its only affected by volume/shape of displaced water and that hasn't changed. So the CB is still at the same spot.

Tried moving the furniture around and that didn't work so extra fixed weight in hull that can't be compensated for is the problem.

Either cut the stern out again and do it with less weight (put the CG back towards the front where it was) or put more buoyancy down at the stern.

Pods at stern intended to bring the CB further back to line up with where the CG now resides (after being dragged towards the back by the transom mods.)

I also agree that adding weight isn't the answer. The reason we've got this problem is from adding weight to the stern in the first place.

I'd be looking really hard at those transom mods. Either cut them out and start again or look at pods for extra buoyancy.

There comes a point though, when we need to realize that by applying band-aids to an injury may end up with more problems from band-aids than from the original injury itself.

[Dignity]

So going back to the very first post, 2 batteries, let say 40 kg was moved to the front to overcome the change in buoyancy and the picture shows still a significant problem. There must have been an awful lot of additional timber and resin used for this to occur.
Nealeboy claims that water in the hull isn't the cause but how he came to this conclusion isn't evident. I've had 2 boats where water got into the hull and an absolute PIA to work out, in one case it couldn't be drained as the bilge area was sealed off to the rest of the hull. In one case the towing eye was letting water through and seeping in below the anchor floor unseen.
Adding pods etc isn't a bad idea but hasn't solved the cause and is only treating the symptom.

[gazza2006au]

Hey Digs Neal has said no water drains out of bung its bone dry after a slip in the wet, the only really thing i can think of as u just suggested a sealed compartment under the floor that doesnt drain to the bilge and out the bung but looking at neals floor layout in that open transom pic it appears he doesnt have a huge cavity under the floor

Neal has told me the transom was rebuilt 5 years ago so maybe he just forgot how deep the hull sat in the water possibly? 5 years is a long time to remember how your boat floated

[Dignity]

Yep, pre pictures don't mean the job was done correctly abd there aren't a couple of sealed areas, I've got 6 sealed areas in my boat, it's by design and water did get into them by a small design fault. A similar boat which sat for years in the open ended up with 150 litres in those areas.
I'd still like some photos of the bilge area,

[blacklab]

pppppppppppppppp

[Lovey80]

This one to me seems super weird. Without looking at the boat in person it is hard to imagine from the photos that a transom re-build could add so much extra weight that moving batteries forward was not an instant fix. Like how much extra ply and resin would you need to add for a 30kg battery being moved forward to not make a difference (It's a rhetorical question Ronje1, no need for a 3000 word thesis to answer).

The sheer amount of resin and ply needed to do this would be overtly obvious. My bet is one of two things:

1. The engine was always too heavy for this hull and the arse heavy attitude wasn't noticed previously.
2. There is a bulkhead or something forward of the drain bungs that is holding water.

The hypothesis that a replaced transom was done so heavy that it was not blatantly obvious just doesn't hold water (pun intended).

[gazza2006au]

I think the full story is not t
With us, the transom was rebuilt 5 years ago so technically we are compairing a 5+ year old memory of how she rode to todays ride

Either that engine was not on there 5+ years ago or someones nemory is vague kind of like your first love

I read chopped mat 1x1m will will soak 1.5 times its weight

My recent transom took around 14-15 litres using chopped mat and cloth

This just isnt working out we are missing the key here