Thursday 26 January 2012

Weight Distribution

As Naughty-Cal is a small planing hulled vessel we have to pay particular attention to how we distribute weight around the boat. Weighing in at just 2.4 tonnes (dry weight) she is extremely sensitive to uneven loading. What appears to be a slight list whilst stationary can turn into an alarming angle of tilt once the boat has jumped up out of the water and onto the plane with the gunnels skimming the surface of the water, quite a scary experience the first few times it happens.

Your average displacement hulled vessel will never achieve fast enough speeds for a slight list to become anything more than an annoyance, however on planing hulled vessels it can become a safety issue if the boat veers off to either side during flight especially if within the confines of a tight river channel.

It took us most of our first summers cruising to get to the bottom of how we should distribute weight evenly throughout Naughty-Cal. Being a small boat you don’t have a lot of choice as to where items can be stored. It was a summer long battle of moving items around until we had achieved a happy medium with the boat sitting almost level port to starboard. Whilst stationary Naughty-Cal does sit slightly bow down as we have a lot of heavy items in the anchor locker, however this does have the benefit of helping her jump onto the plane quicker. The bow is lifted somewhat, by a couple of inches, when we have the dinghy and outboard hung on the transom. This takes some getting used to for a day or two and is especially noticeable when in bed in the midships cabin or when cooking in the galley.

We have just had a particularly thorough clear out of the boat resulting in quite a weight of unwanted items, junk and general clutter being removed from around the boat. It will be interesting to see what effect this has had on both the performance and the trim angle of the boat when we eventually get to open her up again. I suspect we will have a bit of a task getting Cal to sit level again, even though we have made every effort to distribute the weight evenly through the cabin, and it will probably take several attempts to get her planing in a relatively straight line again. This is all part of the parcel of owning a flighty, little sports boat and something we have had to get used to.

The levels of the tank fluids can also have a drastic effect on the trim of the boat. With the black water tank full and the fresh water and diesel tanks getting towards empty Cal sits more noticeably bow down. With the black water tank empty the bow raises significantly. The diesel tank is towards the rear of the boat and at 225 litres has a large effect on the vessels stance. With the tank empty the stern of the boat can be an inch or so higher out of the water. We try to ensure that the diesel and water tanks are topped up on a regular basis to counteract these trim issues but on occasion, whilst out cruising they can run a little low and start playing with the angles of the boat.

As you can see there is more to this sports boating malarkey than first meets the eye. It isn’t always the glamorous pastime that people perceive. A lot of thought, time and effort have to go into the boat before you can begin to start using it to its full potential and enjoying the freedom it brings. We didn’t have a clue how important weight distribution would be when we bought Naughty-Cal and it is only through our own experiences that we have learnt how sensitive to change she really is.

5 comments:

  1. Do you have trim tabs fitted to the boat? If not, get some fitted, they will cure any trim problems.
    Paul

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  2. Yes we have trim tabs fitted but on a small boat they only help so far and according to the manufacturers recommendations should only be used in the fully down position (as the port one would have had to be) at speeds up to 20 knots.

    It is a much simpler and better solution to distribute weight evenly around the boat reducing the reliance on the trim tabs.

    We tend to only use our trim tabs if we have a strong cross wind.

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  4. Hi R.

    When the trim of Rosie goes nose down, (about 2") the water tank 400gals is full and the pumpout tank 260 gals is ready for a suck.

    Might see you in the spring as we are going to be heading south. Thinking of hopping on and off the Trent - doing the Chesterfield and the Foss dyke before heading further south to the Birmingham area.

    take care

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  5. We have a few trips planned for this year so we may see you around. We are heading up to Leeds at Easter, Whitby at Whitsun, Wells in July and then York in September with a few other trips thrown in for bank holidays. Im sure we can catch up at some point during that little lot.

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