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PostPosted: Aug 27th, '18, 21:57 
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CompetentCrew

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Comparing boats to aircraft as far as trim is concerned might be a bit of a stretch. Aircraft have a centre of gravity point which is usually around the spar of the wing and trim is adjusted based on fuel load, passenger load & cargo load. Cargo is loaded with balance in mind via load control, fuel is loaded based on how much fuel is required for the flight plus a reserve and during flight fuel is pumped around the different tanks to keep a centre of balance the the mojority kept in the centre fuel tank. Passengers is where it gets ugly are given seating based on an average weight for an average passenger so they are evenly spread out throughout the aircraft. Trim is so delicate on an aircraft that not so long ago a Qantas 737 took off and the nose was heavy and the Captain trimmed up the nose but was still heavy. After going through system checks the Capt ask the cabin attendant if there was anything unusual in the cabin and discovered a school group was on the plane and about 60 kids were all seated together down the back. The Capt made them spread out throughout the cabin to even out the load. 60 small kids about 30kg each but the computer had them at 75kg each and thats why the aircraft wouldnt trim. If boats were that sensitive the helm would change as crew moved around the boat.


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PostPosted: Aug 27th, '18, 22:45 
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Admiral

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CS, aircraft and yachts have many similarities when comparing the balance of forces'

Like aircraft that change the wing shape to remain efficient at different speeds, yacht's sail shape is adjusted for similar efficiencies at different speeds.

Racers often move crew around the hull to develop different trim in different conditions.

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PostPosted: Aug 27th, '18, 22:50 
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Lakes & Bays Skipper

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Interesting . You realise the helm does change and crew do move around the boat to keep it in trim with the optimum sails set. Especially racing or where you are sailing to a specific destination in the shortest possible time. Strong winds on the Lee rail ,centre on a beat stern running including the helmsman on lighter craft. On the windward rail in very light winds . In close racing the helmsman is constantly giving feedback to the crew on helm feel which can be trimmed by adjusting sails OR repositioning crew.
Some racing boats have water ballast they move from side to side . Others move gear such as sails eg. stack them in the centre behind mast in the cabin. Having a bow heavy boat can cause weather helm. Lots of pilots sail boats. I wonder why.

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PostPosted: Aug 28th, '18, 11:49 
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Inshore Skipper
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"If boats were that sensitive the helm would change as crew moved around the boat."
CS, that's exactly what does happen on small trailer sailers such as our Hartley TS18!

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PostPosted: Aug 28th, '18, 13:44 
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Yachtmaster
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Davidjohn wrote:
"If boats were that sensitive the helm would change as crew moved around the boat."
CS, that's exactly what does happen on small trailer sailers such as our Hartley TS18!


Most definitely the trim changes as I move about on my boat. If I go up to the bow the boat definitely will change course and the automhelm has to make some adjustments to stay on course. It even happens if I leave my seated position at the stern and walk up to the gangway at the cabin. Pretty sensitive I would say.

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