Fore & Aft Trim

[Neil2]

I have a boat in mind which is currently out of the water. Now I know this is useful in that you can see the hull in all its gory detail, but I much prefer to view boats in the canal, apart from them looking ungainly on the hard, you can't tell how the boat is trimmed.

 

It may be just a personal thing, but I can't bear to see narrowboats trimmed bow up, I think they should be virtually level. And it seems to me the ideal is to have the uxter plate just under water when the boat is at rest.

 

Now one thing about the boat in question that bothered me from the start is that an extra roof drain has been cut in the side "cant" at the extreme end of the cabin - and right above a window at that. I couldn't figure why this was, as there is another drain just forward of it - at the point where the bow and stern sheers meet, as it were. Then it occurred to me that if the boat was badly trimmed, instead of the water draining towards the designed drain, some of it would pool at the back of the cabin roof.

 

Fortunately the boat hasn't been blacked recently, so by sighting along the hull from the bow it is just possible to see the waterline, very faint, but it's obvious that the counter sinks well into the water, about halfway up in fact.

 

Digging around a bit more I found a couple of bags of builders sand in the bow storage areas.

 

What is puzzling me is there is nothing in the engine bay other than what you would normally find there, and the engine is the original Lister Alpha, hardly the heaviest engine you will find in a NB. The galley and WC/ shower are amidships, water tank in the bow as usual. So why should the boat have her backside so low in the water unless it's a design fault? To get the counter so low suggests a serious imbalance in weight distribution, something I don't think you could resolve by redistributing ballast.

 

It hasn't been overplated anywhere, by the way.

 

I have seen other boats with the water level at the counter up to and sometimes above the middle rubbing strake, and apart from it looking all wrong it must affect the swim and the handling.

 

The fact that someone has cut a couple of extra roof drains suggests that sorting out the real problem of the stern being too low was either too difficult or impossible to rectify.

 

Does anyone have a view/comment?

 

[nb Innisfree]

Most boats I saw being fitted out looked to be ballasted evenly, confirmed by several I spoke to as being right for a reasonably level boat. After a lot of calculations by me and the missus we arrived at a ballast ratio of two thirds ahead of the middle of the boat and one third behind. Everyone who saw it said it would be bow heavy but we put our faith in our calculations, our faith was justified when it was launched, just slightly bow up. Just before it was launched Pat Buckle agreed with us, the only one who was right.

[BEngo]

I have a boat in mind which is currently out of the water. Now I know this is useful in that you can see the hull in all its gory detail, but I much prefer to view boats in the canal, apart from them looking ungainly on the hard, you can't tell how the boat is trimmed.

 

It may be just a personal thing, but I can't bear to see narrowboats trimmed bow up, I think they should be virtually level. And it seems to me the ideal is to have the uxter plate just under water when the boat is at rest.

 

Now one thing about the boat in question that bothered me from the start is that an extra roof drain has been cut in the side "cant" at the extreme end of the cabin - and right above a window at that. I couldn't figure why this was, as there is another drain just forward of it - at the point where the bow and stern sheers meet, as it were. Then it occurred to me that if the boat was badly trimmed, instead of the water draining towards the designed drain, some of it would pool at the back of the cabin roof.

 

Fortunately the boat hasn't been blacked recently, so by sighting along the hull from the bow it is just possible to see the waterline, very faint, but it's obvious that the counter sinks well into the water, about halfway up in fact.

 

Digging around a bit more I found a couple of bags of builders sand in the bow storage areas.

 

What is puzzling me is there is nothing in the engine bay other than what you would normally find there, and the engine is the original Lister Alpha, hardly the heaviest engine you will find in a NB. The galley and WC/ shower are amidships, water tank in the bow as usual. So why should the boat have her backside so low in the water unless it's a design fault? To get the counter so low suggests a serious imbalance in weight distribution, something I don't think you could resolve by redistributing ballast.

 

It hasn't been overplated anywhere, by the way.

 

I have seen other boats with the water level at the counter up to and sometimes above the middle rubbing strake, and apart from it looking all wrong it must affect the swim and the handling.

 

The fact that someone has cut a couple of extra roof drains suggests that sorting out the real problem of the stern being too low was either too difficult or impossible to rectify.

 

Does anyone have a view/comment?

If the counter plate is in the water it's got too much ballast towards the back. If the bow is up in the air as well it will probably swim like a bucket and there will be a load of unnecessary drag from the counter going forward at an angle.

 

 

You need to see the boat in the water to confirm your suspicions and then to find out how it's ballasted and where the ballast is. The line might just be the result of serious pull-down when going along. For example my counter is on the water standing still, but in parts of Milton Keynes I can easily get the fenders wet. Koukouvagia reports he can rinse his boots when Owl is bracket open.

 

It may be possible to move the ballast forwards and level the boat more. Some bow-up trim when static is needed or the roof will drain forwards when the stern lifts ( in filling narrow locks for example. The pull-down effect of moving forward will make the static bow-up trim a little greater.

 

The effect on gas-locker drains is also important. Too much lowering of the bow might put these underwater, which would mean a need for modification to pass a BSS and ensuring that the newly flooded areas didn't go rusty and start to leak.

 

Once you have the boat in the right attitude then it is time to get the right draft. I think, like you, that the counter should be just under water when standing still. Out of the water means water-slap noises all-night if there any waves. You might need to add ballast or remove it to achieve the right draft.

 

N

[Neil2]

Thanks for that BEngo, by pure fluke I did find a photo of this boat when she was for sale a few years ago, and she does seem to have a somewhat sit up and beg profile. The fact that someone has at some point cut extra drains in the roof channel suggests there wasn't an easy solution to this (I even went to the trouble of phoning the original builder, who says he would never have cut roof drains over a window, but this boat was supplied as a bare shell, unballasted and fitted out by a long since defunct company, so the trail goes dead there)

 

For sure, if you attempted to pull down the bow the gas locker drains would be very close to the waterline, if not under it.

 

There is no extra ballast in the engine bay, but there is a calorifier tank, and dual skin tanks. Under the cabin floor is the usual concrete slab ballast but I can't see how removing ballast from the rear half of the boat is going to make that much difference, the counter looks to be a good 6" lower than it should be, raising the back end by that amount involves taking out some serious weight, wouldn't you think?

 

I'm actually beginning to think she ended up this way right from the start, after all, the builder would get the trim right with all the necessary stuff in the engine bay first, before fitting out inside. I wonder if when they put in the engine, hot water tank, batteries etc, and filled the skin tanks and the fuel tank, she didn't trim level and they couldn't sort it out by adjusting the ballast so that's the reason for the extra roof drain.

 

I did a bit of a search through the archives and did find a reference to other boats from this builder (I don't want to say who it is on the open forum) having similar problems with the roof drainage, presumably for the same reason.

 

The reason I'm getting a bit obsessive about this is I don't want to take on a boat with a trim issue to which there is no solution. If there's just too much weight in the stern for the size and design of the boat, I can't see what can be done.