Fore and Aft Trim

[stranded]

Noticed at the weekend that as currently set up Nooka (Sunbeam 44, disp. 11.3t) appears to be somewhat nose-heavy and as a result rather wetter than I would expect a 44ft cruiser to be in the modest Solent swell outside Cowes on Easter Monday. I imagine this is a combination of beam carried well aft, a lot of heavy stuff up front - 70m of 10m chain, 25kg anchor and windlass in a locker that is very far forward, bowthruster ditto and a hefty watermaker not far behind, lots of stuff like engines quite close to the middle and relatively little aft - expecially at the moment as we have been clearing out a lot of the previous owners stuff and haven't yet filled the space with our own junk - although the water and fuel tanks (about 700l in total) are under the aft bunk. Have been reading a few bits on yacht design and reckon that if I e.g. moved the anchor and chain into an aft locker on long off-shore passages (I can dream) that would raise the bow 3 inches relative to the stern, which would be a start (pain to have to do it on coastal trips though), although 3 inches doesn't sound a great deal. So I suppose I have two questions:

1. Is this more a balance thing - i.e. that modest 3 inch change could sort of tip the see-saw so she sits on her haunches rather than her bow, or is it simply a case that the bow is heavier than the hull form can bear?

2. Related I suppose, if I try to redress the balance by merely weighting up the stern by e.g. sticking half a ton of ballast in a stern locker, rather than weight re-distribution which any way I can figure it is going to be hard/impossible/damned inconvenient, will that help her bow ride over waves or will it just mean that the stern will tend to go through them as well as the bow and we are even worse off!

I am concerned more about safety (and yes damit, aesthetics!) than speed.

Mark

 

[prv]

I'd definitely look to move weight out of the bow rather than trying to counterbalance it in the stern. You may get her flat, but you'll tend to provoke hobby-horsing in the right (wrong) kind of sea, where bow and stern seesaw up and down but the boat doesn't really make progress. That's what happens with smaller yachts, anyway, perhaps 44 feet is big enough to smash on through regardless.

Pete

 

[mainsail1]

Probably time to buy a boat that sits well in the water. My experience is that if they don't sit well they will never sit well. I hope I am wrong in your case!

 

[JimC]

I would concentrate on getting weight out of the bows. Perhaps change to a rope/chain rode? My anchor locker is right forward and if I carry too much chain in it the boat trims bows down.

 

[stranded]

"Probably time to buy a boat that sits well in the water. My experience is that if they don't sit well they will never sit well. I hope I am wrong in your case!"


I hope you are too! At the moment I am clinging to the thought that its hard to imagine the hull would have enjoyed the 13-14 year production run it did if it were so fundamentally flawed (or that she would have been sailed back east across the Atlantic if she had exhibited the sailing characterisitics she did on the way out). Indeed writing this I think I am answering my own question in that if I actually write down the stuff I have removed from the back of the boat that were there when she was in blue water trim: windvane steering, 2 spare anchors, spare propellor, windgen and aquagen, bimini, para-anchor, drogue, 6 man canister life-raft, 20 or 30 gallons of fuel in 6 gerries, stainless 100 litre aux. fuel tank, outboard... that lots got to weigh not far short of 1/2 ton I should think? Obvious thing to do I guess is load up the empty lockers with water (or beer) ballast and try. Still be interested in the answer to the question though whether a tendency to torpedo is a question of absolute weight in the bow or of balance (she sits very nicely on her lines when at rest if that's significant)?

Mark

 

[macd]

Not the least of the consequences is the effect on mast rake. A couple of degrees can make a big difference. Worth checking.

As to pitching/hobby-horsing, as prv wrote, it's self-evident that centralising of mass is far preferable to ballasting the lighter end. Ironically, given what ohmaggie wrote, the consequence of the latter would often be worse in coastal/continental shelf sailing than offshore in the trades, where long following seas are the most likely to be encountered.

 

[stranded]

I would concentrate on getting weight out of the bows. Perhaps change to a rope/chain rode? My anchor locker is right forward and if I carry too much chain in it the boat trims bows down.

I think that might be the other answer. We plan to sail over the horizon eventually but don't particularly want to load her down with cruising kit while pootling around the coast, hence so much removed to storage. 30m chain plus rope should be fine for most coastal situations (I was reading that the Americans and Aussies are far less obsessed with all chain than we Brits, though is that a tide thing?) and when we load up for longer journeys there'll be much more counter-weight in the stern. Think I'll try the water ballast for reassurance that the theory is right and then switch to chain/rope and maybe see how hard it would be to remove the watermaker and store ashore for now - needs an overhaul anyway I imagine, not having been used for two years or more and not likely to be in Channel waters.

Mark

 

[stranded]

Not the least of the consequences is the effect on mast rake. A couple of degrees can make a big difference.

Not sure I quite understand this Mac (still very much a learner) are you saying that lack of mast rake can significantly shift the weight forward, or that having the weight forward and nose down means one has to increase the mast rake to maintain sailing performance, or something else? She is mast-head, which i understand are not generally raked much?

 

[stranded]

Not the least of the consequences is the effect on mast rake. A couple of degrees can make a big difference.

Not sure I quite understand this Mac (still very much a learner) are you saying that lack of mast rake can significantly shift the weight forward, or that having the weight forward and nose down means one has to increase the mast rake to maintain sailing performance, or something else? She is mast-head, which i understand are not generally raked much?

Or is it that the mast sags forward? Causing the forestay to flop? Which might partially explain how I managed to get two spare halyards wrapped both ways round the top of the forestay preventing me from furling (or unfurling to drop) the genoa. That would ease ever so slightly my feeling of foolishness for not tightening them enough.

 

[Daydream believer]

Weight in the ends affects the fore & aft motion & weight would be better in the middle
However considering you cannot see the trim with crew weight in the cockpit the trim may be more level than you realse
I have always preferred bow down trim as it helps( in my experience) performance upwind
If you have a slack forestay it could possibly make furling harder with increased friction
I would definitely get that sorted . Correct Rig tension nearly always has a big effect on performance

 

[Uricanejack]

I would suspect from your earlier posts. you have removed clutter and weight from the stern. this will have affected both your draught and trim.
your boat will be lighter, Sit a bit higher and will have trimed by the head.
your bet is to remove some of the weight from forward and move it aft this will not effect your weight but will reduce your trim by the head.
Many boats are slightly faster trimed down by the head a little. Usualy more difficult to steer.

An old boat I used to sail about 40 ft. long keel and heavy. Carried some movable ballast. large blocks of iorn with handle I think about 50 lbs each
we could adjust trim by moving them.

The best effect of moving weight is from in front of your longitudinal center of floatation to aft of your longitudinal center of floatation.
But if you think in terms of moments ie weight x distance. Any longitudanal movment of weight aft will reduce trim.

On a box shaped vessel or a symetrical vessel. The longitudinal center of floatation is midships. On a real vessel this is rarly true. it also changes with draft.
On a sailing yacht it will be a bit aft of midships due to the aft section of the boat being fuller or having greater bouyancy than the bow.

To get a rough idea. You can do this.

Put a known weight of round No ie 10 or 100 kg on your boat. or just and anchor of 33.5 kg as long as you know the weight. anchors have the weight marked.
measure the distance from right aft to the weights location.
have no one on board.
check and mesure your trim at marked location, you need mark to measure again in same place. the actual position of mark doesn't matter. as long as you can see it. measure distance of water line from boot top. as acuratly as you can.
Now move your known weight a known distance Ie 10 mt aft.
Go back to mark re measure the water line to boot top. it will be diferent dived x 2 and this will be the change of trim.

From this you can work out an aproximate moment required to change trim x 1 cm. using a ratio
trim changed X x moveng Knwon weight 10m
to change trim 1cm how far would you have to move same weight.
A 3 cm change you would have had to move weight a 3rd of the distance or moved a 3rd of the weight.
you dont need to know the center of floatation just the distance from right aft and use moments about this point.
its not complicated
A moment is just weight x dist.
1 kg moved 10 m is the same as 10kg moved 1m

Once you know a moment to change trim 1cm. you can then figure out how much wieght to move how far to change trim to bring boat to an even keel.
or how much to load load where.

Have I ever actualy done this on my boat? No. Just eye balled it.

I'm just adapting a procedure used to load a vessel to even keel. On a ship there are specific draft marks to check trim and the moment to change trim is known.

The designer of your boat probabaly has figured all this out but it is not providedas not needed.

 

[onesea]

Agree with making weight more central, not ballasting the ends...

Then to contradict myself, last boat did not sail well with weight aft present boat hates weight forward. Amazing the diffrence it makes if you just think light forward heavy aft when ever your stowing something... Lots of small things can mount up... Crisps in the forward locker cans aft etc etc...

 

[PeterR]

Have been reading a few bits on yacht design and reckon that if I moved the anchor and chain into an aft locker on long off-shore passages (I can dream) that would raise the bow 3 inches relative to the stern, which would be a start (pain to have to do it on coastal trips though), although 3 inches doesn't sound a great deal.

I have a 34 footer with 60metres of 10mm chain and a 15 kg anchor. Putting the anchor and chain in the bow well only raises the water line by a couple of inches. Filling the bow water tank makes another couple of inches difference and thats on a boat with a very fine entry. I doubt moving the chain on a 44 footer would make any significant difference to the waterline but I guess the only sure way to find out is to try it and see

 

[Rossynant]

Problem is not so much about trim and weight placement along, as concerned with mass at bows, inertia of fore part. Modern shape boats have little reserve buoyancy forward, while pivoting point is not at hull middle, but somewhere in widest flat stern. So a lever is long, so to say. Bow gets reluctant to lift on a wave. This actually is good for speed to windward, at least in moderate conditions. But wet...
Taking some heavy stuff from bow should help, specially from the very tip. Ballasting the rear would have no effect.

 

[macd]

ohmaggie: sorry about delay in getting back to you.
What I was saying is that if the boat is, say, 2 degrees down at the bow then (unless the rig's been tweaked to compensate), then her mast will also have leaned forward by 2 degrees. The effect of this is by no means certain, but it moves the sails' centre of effort forward which is likely to reduce weather helm/increase lee helm. Ideally you want a touch of the former and none of the latter, so that left to her own devices she will tend to gently turn into the wind. There are no absolutes, but masthead rigs typically lean back by perhaps 12-18 inches for what I guess is the size of your mast. The proof of the pudding's in the way she handles.

 

[d4raffy]

I think its just an illusion - Solent swell is more likely to spray up - especially on cold easter days!
Sunbeams are for warmer climes - Caribbean or Med cruising. You need to distribute appropriate number of bikini clad crew - sun bathing on that large aft deck.
Once the beer and rum is loaded and the ice maker is going it balances out nicely. Just sit aft with your G&T using your wireless autopilot - works for me.

yours ... Another Sunbeam 44 owner ;-)

PS ... thats what those 4 huge stern lockers are for.

 

[stranded]

Thanks so much for all the good advice. I wonder also whether the different perspective from a centre cockpit meaning one is looking more down at the bow than from a lower aft cockpit affects the perception. Certainly she handles very nicely, with just a touch of weather helm and very easy steering now we've had it serviced. Point taken about relative ineffectiveness of counterbalancing the stern, although difficult to imagine that all that heavy weight up front but currently 3 out of 4 large aft lockers more or less empty is not going to have some effect. It could be a perfect excuse to go shopping. Except I really think I should try d4raffy's solution. Just in case...