Weight in the ends of a Boat

[jac]

It seems to be generally accepted that weight in the ends of a boat is a "bad thing." I don't understand why. Can anyone explain?

I can fully see why weight per se is a bad thing - it slows you down. Equally I can see why all the weight at one end would be bad as it would affect the fore and aft trim and make handling a nightmare.

I remember reading a book by Ian Nicholson ? which stated that weight in the middle made a boat faster to move in both pitch and yaw whilst adding at the ends, slowed these turning speeds. Is that right?

And assuming that the overall weight is the same and that trim is unaffected, why is weight at the ends bad?

 

[Lon nan Gruagach]

It seems to be generally accepted that weight in the ends of a boat is a "bad thing." I don't understand why. Can anyone explain?

I can fully see why weight per se is a bad thing - it slows you down. Equally I can see why all the weight at one end would be bad as it would affect the fore and aft trim and make handling a nightmare.

I remember reading a book by Ian Nicholson ? which stated that weight in the middle made a boat faster to move in both pitch and yaw whilst adding at the ends, slowed these turning speeds. Is that right?

And assuming that the overall weight is the same and that trim is unaffected, why is weight at the ends bad?

Technical term: Moment of inertia.
Simple terms: pick up a 1 lb weight, now put it at the far end of a stick half the length of your boat and pick it up. Not so easy, is it?
So, if its ballast you are after but dont want to make it difficult to pitch and yaw, then put the weight in the middle.

 

[jac]

Technical term: Moment of inertia.
Simple terms: pick up a 1 lb weight, now put it at the far end of a stick half the length of your boat and pick it up. Not so easy, is it?
So, if its ballast you are after but dont want to make it difficult to pitch and yaw, then put the weight in the middle.

Thanks

Although a completely unscientific recollection of seeing other boats in a bit of chop suggests that they hobby horse a lot. SO would distributing the weight to the ends increase the moment of inertia and therefore reduce hobby horsing.

 

[Poignard]

Weight at the ends makes the boat slower to pitch. I used to keep my 35lb anchor in the bow roller but now I have it lashed on the foredeck in chocks. I have also got rid of the two Calor gas bottles in the after ends. The difference in the boat's motion is very noticeable because she now rides the waves instead of ploughing into them.

 

[Deleted member 36384]

... I have also got rid of the two Calor gas bottles in the after ends. .... .

What size were the Calor Gas bottles as I have 2 on the stern but they are only the 3.9kg/8.5 lbs size. I am wondering if that would make such a big difference.

 

[lw395]

Weight in the ends takes more force to accelerate it.
Say your boat hits a wave which lifts the bow a foot. More mass in the ends means it will take more force and lift slower.
So it will hit the wave harder and slow you down more.
I can't see that as a cure for hobby-horsing.
I've heard it said in some dinghies it can be good for the helm and crew to sit apart, to stop the chop from upsetting the rig. But generally the rule is keep the mass concentrated and let the boat follow the waves.

Equally it's all about steering in the best way to drive around/through the waves.

 

[NormanB]

Weight at the ends makes the boat slower to pitch. I used to keep my 35lb anchor in the bow roller but now I have it lashed on the foredeck in chocks. I have also got rid of the two Calor gas bottles in the after ends. The difference in the boat's motion is very noticeable because she now rides the waves instead of ploughing into them.

Don't you mean weight further to the end would make it MORE prone to pitch and faster to pitch.

 

[NormanB]

Weight in the ends takes more force to accelerate it.
Say your boat hits a wave which lifts the bow a foot. More mass in the ends means it will take more force and lift slower.
So it will hit the wave harder and slow you down more.
I can't see that as a cure for hobby-horsing.
I've heard it said in some dinghies it can be good for the helm and crew to sit apart, to stop the chop from upsetting the rig. But generally the rule is keep the mass concentrated and let the boat follow the waves.

Equally it's all about steering in the best way to drive around/through the waves.

I think you have that arse about face.

The weight is on a beam at the greater distance from the centre of flotation so will rotate about that point any small addition of weight or force is acting on a long lever. That's why designers aim to centralise mass as far as is practically possible. Moving the anchor and cable as far aft as possible and moving other wights towards midships is the aim.

 

[Poignard]

What size were the Calor Gas bottles as I have 2 on the stern but they are only the 3.9kg/8.5 lbs size. I am wondering if that would make such a big difference.

4.5kg but that is only the weight of the gas and the tare weight of the container has to be added to that

https://www.calor.co.uk/4-5kg-butane-gas-bottle.html

 

[Poignard]

Don't you mean weight further to the end would make it MORE prone to pitch and faster to pitch.

I meant less responsive, because of inertia.

 

[Deleted member 36384]

4.5kg but that is only the weight of the gas and the tare weight of the container has to be added to that

https://www.calor.co.uk/4-5kg-butane-gas-bottle.html

What was the gross weight that you removed from the stern and the size of boat. I don't think 20 kg about 6 m back from the COB will make much difference but I am not sure, hence I am trying to get a feel for the weights that you moved as you stated it made a noticeable improvement. How far back did you move the 35lb anchor?

 

[lw395]

I think you have that arse about face......

No.

 

[lw395]

What was the gross weight that you removed from the stern and the size of boat. I don't think 20 kg about 6 m back from the COB will make much difference but I am not sure, hence I am trying to get a feel for the weights that you moved as you stated it made a noticeable improvement. How far back did you move the 35lb anchor?

I found a noticeable, mesurable improvement moving the anchoring and rode from the anchor locker to near the base of the mast on a 40ft boat. Easier motion and at least 0.1 knot more through the water. This was beating into typical swell in Christchurch Bay.

 

[Lon nan Gruagach]

The benefit or not of having heavy ends depends on more than just the absolute inertia. As lw395 posted earlier, it will make a boat slower to rise, but when it goes it will come down harder and hit the wave deeper.
What you have is a tuned pendulum. By varying the weight distribution you could set for a flat ride or to "go with the flow" and follow the waves. Just what the setting is depends on the frequency of the waves.

One thing for sure though, heavy ends will make steering less responsive.

 

[Deleted member 36384]

I found a noticeable, mesurable improvement moving the anchoring and rode from the anchor locker to near the base of the mast on a 40ft boat. Easier motion and at least 0.1 knot more through the water. This was beating into typical swell in Christchurch Bay.

Thanks's for that, that's tangible and would be wroth the effort of an anchor chain box at the mast, down below. I have gone from a 60lb CQR to a 40lb Knox but moved the chain locker forward by 2' to get a better drop. I do have a plan for an anchor chain box at the mast base between the saloon end and table end if I go long offshore - manual transfer. I guess it all adds up and the sum of lots of small things can be quite significant at the end of the day.

 

[jwilson]

Long long ago I tried to cure hobbyhorsing in the short and very lumpy wind-against-tide seas of the Bristol Channel by moving heavy stuff to bow and stern. Definitely reduced pitching but increased "slamming" and overall slowed the boat down.

 

[Poignard]

What was the gross weight that you removed from the stern and the size of boat. I don't think 20 kg about 6 m back from the COB will make much difference but I am not sure, hence I am trying to get a feel for the weights that you moved as you stated it made a noticeable improvement. How far back did you move the 35lb anchor?

I don't have the boat by me at the moment but I think moved the anchor back about 3 feet. My 28-foot boat has a cutaway forefoot and a steeply sloping transom. She has a narrow beam by modern standards so there is not a great deal of reserve buoyancy. I have a heavy windvane mounted right aft, and an outboard motor; too much weight really but I have nowhere else to put the outboard and the windvane obviously cannot be moved. I think shifting the anchor back made most difference.

 

[Halo]

My understanding is that the reason the old time sailors were very keen to keep weight out of he ends of boats was to preserve the boat in adverse conditions. If you stand at the pulpit when beating into a heavy chop you will feel the acceleration (as heavy and lighter weight ) as she pitches. This acceleration up and down puts stress into the hull in proportion to the weight at the ends. Hence the desire to keep weight out of the ends.
As I recall Lord Cunliffe referred to this in his TV programme about Bristol Channel Cutters

 

[Kermit]

Reminds me of when Dennis Conner all but accused Chris Dixon of building the Kiwi boats out of fibreglass to cheat the rules. He claimed that every other 12 meter had been aluminium which is easier to test the thickness off. I believe that the rules for 12m boats say that the hull must be of uniform thickness.

Conner offered to drill holes in the New Zeland boats to check the thickness. Dixon said "over my dead body" to which Conner replied "that's fine by me" or something similar.

You don't seem to get the characters like Conner, Blackaller and Turner in the sport these days.

 

[TQA]

My totally unsupported gut feeling that weight in the ends might matter if you have a small light weight used for racing and where 2 seconds a mile is a big deal.

If like me the 2 x 50 lb anchors plus 400 ft of 3/8th chain can stay on the bow along with the RIB. while the 100 lbs OB is mounted on the pushpit under a gabtry with 400 watts of soar and a transom locker with 2 x 20 lb gas bottles can stay there as well..

Me boat goes just fine, I is a cruiser.