10mm v 15mm Base plates

[Boondock]

Hi all,

 

As the title really, can anybody give me the advantages and disadvantages of the differing thickness of base plates. I'm thinking of having a 10mm one but have an option for the thicker version.

 

Many thanks in advance.

 

Boondock

[Proper Job]

A thicker baseplate means less ballast is required in the finished boat. This could potentially mean that the floor can be lower (although to some extent, the cross bearers will determine this) which in turn will give more head room in the cabin.

 

It's highly doubtfully that it will extend the life of the hull as the main corrosion point is at the water line.

[RLWP]

Personally, I think the 10mm/15mm thing is a fashion statement. Does the 15mm baseplate use thinner floor bearers? If not, there's no advantage in having less ballast as you don't get any useful space back.

 

Richard

[alan_fincher]

Hi all,

 

As the title really, can anybody give me the advantages and disadvantages of the differing thickness of base plates. I'm thinking of having a 10mm one but have an option for the thicker version.

 

Many thanks in advance.

 

Boondock

Just my view.....

 

Whilst in theory, eventually a 10mm base plate will have thinned enough to need some re-plating work, the reality is that unless you constantly drag it through the shallows, or take it in particularly contaminated waters, you are talking a very very long time for this to be necessary.

 

The main advantage of a thicker base, to me, seems to be that less ballast is then required, but I often find that argument slightly spurious, as most boats are constructed with the bottom "girders" about 4" tall, and generally the void this creates is more than adequate for any ballast needed. I can't really follow the argument that less ballast can mean greater internal headroom, if the wooden floor still sits 4" above the baseplate, because of the framing steelwork.

 

Some have suggested that if the base-plate needs to be made from jointed plates this gets progressively harder for the fabricator, the thicker they go. Some fabricators have been known to skimp on welding the joints between base-plates, only welding from the "top", as they don't have the wherewithal, (or the inclination!), to "flip" it over and "vee" and weld the other side. Worth checking what your builder does.

 

If you can buy 15mm for no more additional cost than the extra ballast you would need if you had gone 10mm, then it would make sense to me to use the thicker. Not sure I'd pay a huge premium for it, though!

[Proper Job]

Just my view.....

 

Whilst in theory, eventually a 10mm base plate will have thinned enough to need some re-plating work, the reality is that unless you constantly drag it through the shallows, or take it in particularly contaminated waters, you are talking a very very long time for this to be necessary.

 

The main advantage of a thicker base, to me, seems to be that less ballast is then required, but I often find that argument slightly spurious, as most boats are constructed with the bottom "girders" about 4" tall, and generally the void this creates is more than adequate for any ballast needed. I can't really follow the argument that less ballast can mean greater internal headroom, if the wooden floor still sits 4" above the baseplate, because of the framing steelwork.

 

Some have suggested that if the base-plate needs to be made from jointed plates this gets progressively harder for the fabricator, the thicker they go. Some fabricators have been known to skimp on welding the joints between base-plates, only welding from the "top", as they don't have the wherewithal, (or the inclination!), to "flip" it over and "vee" and weld the other side. Worth checking what your builder does.

 

If you can buy 15mm for no more additional cost than the extra ballast you would need if you had gone 10mm, then it would make sense to me to use the thicker. Not sure I'd pay a huge premium for it, though!

 

As I spend most of my time dragging through the shallows of the Southern Oxford, I do take some comfort in the fact that I do have a 15mm base plate. I wonder how much erosion of the base plate happens by doing this. There must be a fair few gouges in it by now and the rest of it must be fairly shiny.

 

 

Being 1.5 times thicker, surely it would be about 1.5 times more expensive?

Edited September 27, 2010 by Proper Job

[RLWP]

As I spend most of my time dragging through the shallows of the Southern Oxford, I do take some comfort in the fact that I do have a 15mm base plate. I wonder how much erosion of the base plate happens by doing this. There must be a fair few gouges in it by now and the rest of it must be fairly shiny.

 

 

Being 1.5 times thicker, surely it would be about 1.5 times more expensive?

 

Are you seeing any chamfering of the edges of the baseplate when you dock her? That's what happens to hire boat hulls from frequently being out of channel

 

Richard

[Timleech]

 

 

 

Some have suggested that if the base-plate needs to be made from jointed plates this gets progressively harder for the fabricator, the thicker they go. Some fabricators have been known to skimp on welding the joints between base-plates, only welding from the "top", as they don't have the wherewithal, (or the inclination!), to "flip" it over and "vee" and weld the other side. Worth checking what your builder does.

 

 

 

There's no reason why the bottom plates need to be welded from both sides, it's quite possible to do a proper job from one side only. That said, 15mm would need some fairly heavy prepping to do it properly, and there's no guarantee that it will be done properly. OTOH I suppose that applies to all the welding

 

Tim

[Boondock]

Many thanks for the prompt responses.

 

Not sure on the price difference yet although I'm sure there will be one, you don't usually get anything for nothing on a new build!

 

My feeling was for the 10mm plate and currently I'll stick with that.

 

Slightly off topic I'm assuming that when re blacking the hull the base plate is omitted?

 

Thanks again for the information

 

Boondock

[bargeeboy]

Many thanks for the prompt responses.

 

Not sure on the price difference yet although I'm sure there will be one, you don't usually get anything for nothing on a new build!

 

My feeling was for the 10mm plate and currently I'll stick with that.

 

Slightly off topic I'm assuming that when re blacking the hull the base plate is omitted?

 

Thanks again for the information

 

Boondock

 

We have settled for 12 mm base plate on all our new boats and shells.

 

No point in 15 mm base plate and 6 mm sides ! if going to 15 mm 8 mm sides would be expected.

 

We also put 3 coats of paint on the underside of the base plate in the factory which I consider is good enough for 10 years wear on a 'shallow' drafted boat even if it is never done again.

Edited September 27, 2010 by bargeeboy

[Keeping Up]

Although it is 'only' 12mm, thick, the weight of our base plate meant that no additional ballast was needed. This led to floor bearers of just 1" or so , which can be seen in this photo taken during construction.

 

 

 

The floor sits directly on these, which means that we have well over 6ft 3in of headroom even though our roof-line is lower than most modern boats and our draught is less than 2ft.

 

The boat-builder normally offered choice of 6mm (for cheapskates) 8mm (the standard) or 10mm (at extra cost). He was amazed when we asked for 12mm but It actually worked out no more expensive than the 10mm option because of the money saved on floor bearers, ballast, etc.

 

Apart from the headroom advantage, and the peace of mind that even the most stubborn shopping trolley is unlikely to bend the baseplate, it means that all the weight is concentrated very low down (not just because of the baseplate being the ballast but also because everything sits on a floor which is lower) sp the boat is very stable. Whether or not the additional stiffness is an advantage, I have no way of telling.

 

I would go for the thicker option.

[casper ghost]

Isn't there an issue with having to heat the thick steel when welding to other steel sheet that is less than half it's thickness, eg 15mm to 6mm.

Casp'

[Neil TNC]

Hi all,

 

As the title really, can anybody give me the advantages and disadvantages of the differing thickness of base plates. I'm thinking of having a 10mm one but have an option for the thicker version.

 

Many thanks in advance.

 

Boondock

 

There is one other benefit of having a thick, 15mm baseplate, that is stability....this would only really be of use if you are going to do any serious tidal stuff in your NB. AFAICR, talking to James Griffin - seagoing NB Ocean Princess had no slab ballast. It had a 15mm baseplate back to where the rear swims started, then went to 10mm. Any trim ballast was done by 15mm steel plate tacked onto the inside of the bottom plate. I can testify that Ocean Princess was incredibly stable and balanced, it rode waves like a proper little ship, with out the normal bow thrashing and slamming that most other NB's would do when faced with some rough seas. It also seemed very stable on canals and was less prone to rolling. As for welding 15mm bottom plate to 6mm sides, I have been told by more than one fabricator, this is no problem if you have the correct and properly rated welding equipment. If you had a 15mm baseplate and are not worried about increased headroom, you could have a lower cabin, making some of the lower bridges on the far flung waterways possible / easier.

Would I do it?...probably not!...if I did, it would be for the lower profile option....because I know how near the limit NB Earnest was on some of the bridges out in Fens and Witham Navigable Drains.

[Keeping Up]

There is one other benefit of having a thick, 15mm baseplate, that is stability....this would only really be of use if you are going to do any serious tidal stuff in your NB. AFAICR, talking to James Griffin - seagoing NB Ocean Princess had no slab ballast. It had a 15mm baseplate back to where the rear swims started, then went to 10mm. Any trim ballast was done by 15mm steel plate tacked onto the inside of the bottom plate. I can testify that Ocean Princess was incredibly stable and balanced, it rode waves like a proper little ship, with out the normal bow thrashing and slamming that most other NB's would do when faced with some rough seas. It also seemed very stable on canals and was less prone to rolling. As for welding 15mm bottom plate to 6mm sides, I have been told by more than one fabricator, this is no problem if you have the correct and properly rated welding equipment. If you had a 15mm baseplate and are not worried about increased headroom, you could have a lower cabin, making some of the lower bridges on the far flung waterways possible / easier.

Would I do it?...probably not!...if I did, it would be for the lower profile option....because I know how near the limit NB Earnest was on some of the bridges out in Fens and Witham Navigable Drains.

 

Agreed about stability. Keeping Up proved to be remarkably stable when the waves go up a bit on the Sharpness-Portishead run.

 

 

 

 

 

 

 

As for the Fens:

 

 

[Neil TNC]

 

As for the Fens:

 

 

I don't think it is off topic, I think airdraught is very important in a boat, and can relate to baseplate thickness...you should see the fun I am having with Barge Maurice A!

 

NB Earnest never fitted Ramsey Hollow before it was raised, it would now.

 

We did manage to do it in NB Frogmoore II, an official TNC Fleet Auxillary.

 

We did manage Exhibition Bridge on the River Nene Old Course (level down), is that tight or what!

Edited September 27, 2010 by Neil Arlidge

[bag 'o' bones]

Its all well and good installing a 12-15 mm baseplate to reduce the amount of ballast required but what happens if you need to rearrange the ballast to take into account the fitting of heavy fixtures and fittings? I thought that was the whole idea of having movable ballast?

[Proper Job]

A thicker base plate will bring the overal depth of the boat down. You may still need to add ballast to trim the boat. That should be minimal though.

 

A thick base plate does keep the C of G as low as possible. When floating (not often on the canal system), Ocelot barely moves when people get on/off.

[Neil TNC]

Its all well and good installing a 12-15 mm baseplate to reduce the amount of ballast required but what happens if you need to rearrange the ballast to take into account the fitting of heavy fixtures and fittings? I thought that was the whole idea of having movable ballast?

 

AFAIK people with 15mm baseplates, using the extra height available, use bits of 15mm plate as trim ballast.

[mrsmelly]

Hi all,

 

As the title really, can anybody give me the advantages and disadvantages of the differing thickness of base plates. I'm thinking of having a 10mm one but have an option for the thicker version.

 

Many thanks in advance.

 

Boondock

 

 

Blimey what a scarey thought a boat with only a ten mill base plate who the hell builds such a tinny thing you will tell me the cabin is only 4 mill next..........

The main reason for a heavier base plate is a very low centre of gravity which gives greater stability at all times, when mates who have tin foil boats get on mine they often observe and remark how it doesnt rock getting on and off and moving about. Also My roof line is lower than most other boats but still plenty of headroom and no balalst needed we just have a few engineering bricks fitted for trim where needed. As for longevity I agree that in the real world 10 mill will outlive most of us anyway but still wanted 15 mill for all other reasons.

[Guest]

My boat has a 10mm baseplate,and loads of bricks for ballast. Presumably if it had a 15mm base plate then there would not need to be any bricks. I think that would be a vast improvement as when (not if) the boat does get flooded, it will be much easier to pump out and dry everything out afterwards. I would have gone for a 15mm baseplate and done away with bricks had the option been there, at a sensible price.

[alan_fincher]

when mates who have tin foil boats get on mine they often observe and remark how it doesnt rock getting on and off and moving about.

AS it's a Hudson, it probably doesn't rock 'cos it's sat on the canal bed!

 

As for moving about, don't you need diesel in your tank to do that ?

[hughc]

Wyrd was built twenty odd years ago with a 20 or it might be 22 mm baseplate in order to ensure that we had a 3' water draught over the whole 55' to aid towing. The boat is very stable and certainly gaffers anything hung on the back. On dock there has been no visible wastage of the chine; the edge of the bottom is as sharp as the day GT Boats delivered it. It does mean that we kept the air draught down to 5'1" which was the aim in order to pass through Froghall before the pound was lowered and it has enabled us to get through some very low bridges on the Drains. My sons at 6'2" and 6'3" have ample headroom and I have standing headroom in the back cabin. It seems to me that modern designers are far to timid. Deeper draught boats with longer swims and narrower base plates are more stable, swim better and are warmer in winter and cooler in summer. Nor is speed compromised and we have never been stopped by lack of depth anywhere and that includes the Llangollen and the Chesterfield. Shallow draught boats are not the answer they are only a short term fix. Regards, HughC.

[Steve Goddard]

I had this conversation when I started Siskin and decided to go the 10mm route. Why? Well first of all I had no real idea of what my final draft would be, how the boat would end up trimmed fore /aft after the fit-out and what the final displacement would end up as. I know that I will need ballast (probably 3.5 tons) and now I know that no matter what I end up with I can get it right. If you have 15mm plate and you have too much weight at one end it's really difficult to take it out I'm not convinced about the additional stability that a thicker base plate would afford. If you are using say a single layer of engineering bricks as ballast you would only raise the CoG of the ballast by less than 2" given that the fore / aft yaw axis of the boat as a whole is probably a couple of feet off the base plate I suspect that the shape of the hull has more to do with the pitch and roll than the position of the ballast. If you really want to cut rolling down dramatically have a keel

 

I agree wholeheartedly that base plates should be welded top and bottom to ensure full penetration and to avoid potential corrosion pits. It's actually not a big job for anybody who can weld overhead. I've watched the side plates being welded to the bottom plate on Siskin and the difference in thickness is simply not a problem. Providing they are welded from both sides of the side plates you get a full penetration on the side plates and a similar penetration into the base plate and as far as I can see the weld will probably outlast the rest of the boat.

[mrsmelly]

AS it's a Hudson, it probably doesn't rock 'cos it's sat on the canal bed!

 

As for moving about, don't you need diesel in your tank to do that ?

Thanks alan

 

Thought I could rely on you, will I ever get over the running out of diesel thing ?..............and hey mines only got a 2 foot six draught so not like Pjs which is about 14 feet.....

 

I had this conversation when I started Siskin and decided to go the 10mm route. Why? Well first of all I had no real idea of what my final draft would be, how the boat would end up trimmed fore /aft after the fit-out and what the final displacement would end up as. I know that I will need ballast (probably 3.5 tons) and now I know that no matter what I end up with I can get it right. If you have 15mm plate and you have too much weight at one end it's really difficult to take it out I'm not convinced about the additional stability that a thicker base plate would afford. If you are using say a single layer of engineering bricks as ballast you would only raise the CoG of the ballast by less than 2" given that the fore / aft yaw axis of the boat as a whole is probably a couple of feet off the base plate I suspect that the shape of the hull has more to do with the pitch and roll than the position of the ballast. If you really want to cut rolling down dramatically have a keel

 

I agree wholeheartedly that base plates should be welded top and bottom to ensure full penetration and to avoid potential corrosion pits. It's actually not a big job for anybody who can weld overhead. I've watched the side plates being welded to the bottom plate on Siskin and the difference in thickness is simply not a problem. Providing they are welded from both sides of the side plates you get a full penetration on the side plates and a similar penetration into the base plate and as far as I can see the weld will probably outlast the rest of the boat.

Hi

 

If u are not convinced then give me a ring and I will take you for a spin on my boat and you will experience how much better the stability is, and of course it is greatly helped by the steel keelson and solid steel not hollow stem post etc. Also with my swims at 14 feet when underway we cause virtualy no wash.still no matter all boats are great my first was quarter inch steel and we loved it.

[Sunset Rising]

despite the fact that I do not have a narrowboat yet and therefore know not of what I speak, it seems to me that all of you are totally missing the point.

 

Thick base = no balast = cool/cold storage space in the bilges just the right size for bottles of wine.

 

No ?

[Keeping Up]

Not when you use the lack of ballast to lower the floor to within an inch of the base. I've had to find alternative storage space for my beer and wine.