Gemini 105MC Slow speed under power - Page 4 - SailNet Community
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post #31 of 82 Old 04-25-2010
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Quote:
Originally Posted by TexasWill View Post
To the best of my knowledge we at about 45 degrees into the wind. The wind was about 9-11 knots, and we were sailing 3-4 knots. Then we tacked switching the wind off the port side (still at 45 degrees) and kept the same speed. Then we motored back.
It is not just the motor then, it's a deeper issue.

9-11 kts of wind close hauled should get you 6 kts or better.
This isn't me bragging on my boat, this is the very real performance expectations.
This is a polar chart done up by one of the owners (Isis) - a owner who is well regarded, an aeronautical engineer, and a personal acquaintance of mine. I have tested it to the limit of my ability and the winds - it's real.



The example given is a good one - at 40 degrees apparent and 12 kts of TRUE wind you can and should expect 7.3 kts of boat speed, clean bottom, decent sails and proper trim a given.
I've topped 10 kts in 16 true, GPS and log confirmed, including photo's on this forum- and I'm loaded to cruise, dinghy, AC etc.
Three weeks ago, with a 15 month old bottom paint job my Admiral (MMR posting above) and I topped 6.5 kts in 12kts apparent - "light" loaded, no dinghy on the davits, no bedding, light liquids on board.

The polar uses jib and main - Isis doesn't have a screecher. I was using mine when I busted 10 knots, but not in the example above.

I am not aware of a lake capsized Gemini by an owner. I'd appreciate it if you PM'd me the name and hull number - I don't ask for me; there is a club called the Gemini Gem's, which consists of many of the owners. We'd like to know the story as it is pertinent to us (any Gem's story of a capsize is good to us for information purposes).

78k in receipts for a 2001? That is a seriously large amount of repairs for a Gemini. I paid 145k for mine new in 2007 (More with options -23k in add ons - 168 total). Current base price is 192k.
One Note, a 105M sank at the pier under snow this year 5 miles from my slip, it was totaled for less than that. Just saying.

I don't want to spook your deal, if you like the boat you like the boat. I love mine, minus some quality control issues.
I was told there was a Gemini thread here with some speed issues, figured I'd present some info.

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post #32 of 82 Old 04-25-2010
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the repair invoices didn't have any line items for 'ballast', did they?

Is there a way to measure draft, or freeboard? what else but excess weight or incredible drag could make it that slow under both power and sail?
One big honking barnacle?

I would be extremely interested in knowing where I can find info on the bareboat charter capsizes. We have our first charter on one in a few weeks.

What does it take to flip one of these? Not reefing enough and tripping on a centerboard?

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Last edited by 2Gringos; 04-25-2010 at 08:18 PM.
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post #33 of 82 Old 04-25-2010
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2Gringo's,

To my understanding, one flipped in San Diego two years ago. A bareboat skipper, wife and child onboard, no injuries.
He was going downwind in 25 knots, full sail and screecher - pulled in sails to gybe and turned 90 degrees (broad side on) with sails tight; and got hit by a 4 foot wake at the same time.

To flip one you have to get one hull up past 19 degrees (it leaves the water at 18 degrees of heel). At that point you have wind under the hull. If you do nothing you will go over.
By the chart above, that takes full sail in 28 knots of true wind 90 degrees off the wind and the sails have to be in tight so the pressure does not bleed off as speed (i.e., all heeling force).

Testing at PCI says at 85 degrees it will come back down right side up, if there is no wind. Ha.

I've sailed mine close hauled in 22 kts with jib and main full. I was heeled about 6 degrees; I took a reef in the jib by 1/3 and leveled out to 3 degrees and gained 3 knots of speed.
The designer recommends no more than 7 degrees of heel should be allowed.

Following the reefing points - most importantly - on a catamaran you reef for the gusts not the steady wind. To be clearer, if the forecast is 15-20 an gusts to 25, you reef as if it's all 25 (first in jib, first in main for certain, 2nd in jib if you are going to wind).

And you always mind your heel. It's a skinny cat. Skinniest one on the market. 40 foot mono's have the same beam.
4 are circumnavigating, many have crossed the pond.
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Last edited by chucklesR; 04-25-2010 at 08:35 PM.
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post #34 of 82 Old 04-25-2010
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I'd point out that the hulls can't be misaligned unless the bridgedeck was severely damaged and they had to re-join the two hulls to some degree. The two hulls and the bridgedeck's lower half are made in a single mold AFAIK, and the deck is a single mold as well.

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post #35 of 82 Old 04-25-2010
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Hey chuckles! Sup dude?

I drove a Corsair 31 this weekend. Freakin' fast. 17 knots downwind with a screecher (Code 0).


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post #36 of 82 Old 04-25-2010 Thread Starter
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I may have had the wind speed mixed up( to be honest I wasn't really looking at the instruments that closely) but armed with your chart I am sure we can get some very accurate readings this tuesday. Thanks, chuckles, I now feel confiedent that between myself and the surveyor we will be able to tell if anything is wrong under sail. I feel much better already.

How hard is it to achieve these speeds? Are these expected speeds or maximums? How much of a margin could be generated by sails not properly trimed or any other error a novice sailer may make?

Last edited by TexasWill; 04-25-2010 at 11:08 PM.
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post #37 of 82 Old 04-26-2010
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TexasWill:

Polar charts are projections of performance based on getting it right. Racing skippers use them to set goals. The maker of that chart gave permission to use it (copyright) but not the full write up. A reasonably skilled and attentive skipper with reasonably not blown sails and reasonably loaded boat should get within 10% or so.
If in the example of 12 kts true you aren't making 7.3kts and instead make 6.5 I'd call it a good day. BUT it should make at least 6kts.

Suffice it to say, the sails are 9 years old, the skipper is a factor (familiarity etc). The standing rigging needs tuning etc.. it's not a racing boat.

10kts true should get you 6; Point up, trim, then fall off to a reach. If I can't make 2/3 of wind speed on a lazy haul at 60 off I've had too much Rum or there is a bikini nearby.

My demo sail sold me on the boat, 6 kts of wind outside Annapolis; main and screecher we made 4kts at 35 off the wind. Sailed a circle around a schooner that was slapping and flapping trying to make enough way to turn.

One other note, this might help with fairness of helm. The boat should balance out with almost no weather or lee helm at all. If she has rudder position indicators on the auto helm note them - sailing hard into the wind should be one bar on the indicator, no more.
If it doesn't have a indicator all is not lost: pop the rudders up and eyeball center, put a piece of tape on the wheel. Hard into the wind should be no more than 1/3 turn of the wheel.
I can almost always play the sails and get neutral helm.
Heck you can sail totally using the traveler to turn the boat if you want and know how. I do it all the time (sitting on the hammock).
You should pop up the rudders anyway just to check that both are tracking.

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One possible problem that can be an issue is if the rudders aren't parallel to each other. That can cause severe drag and slow the boat considerably. You really want to check that the rudders are aligned with each other. If work was done to the boat's steering system, this could easily have been screwed up and not checked.

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post #39 of 82 Old 04-28-2010 Thread Starter
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We had the Survey yesterday and it did include a haul out. The bottom was spotless, the centerboards and rudders we all in good shape and aligned. The surveyor measured and poked and said there was nothing wrong with the hull that could cause the slowness. I did get some measurements under sail. The surveyor said the rigging was very loose, and that may account for the slow speed under sail, but here they are;

90 degrees, 12 knots of true wind. 5.2 knots boat speed
70 degrees, 10 knots of true wind. 5 knots boat speed

We tested with a portable Tac and the engine was matching up with the instrument reading.

2000 RPM 3.3 knots
3000 RPM 4.7 knots
3600 RPM 5.2 knots

We also tried to get a read from the portable tac on the back side of the transmission, but the measurements were all over the place, and over half the time that tac didn't even read. We are thinking this means the transmission is slipping, but we need to get an engine surveyor to verify it. Thoughts?

-Will
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post #40 of 82 Old 04-28-2010
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Will

we looked at the Gemini very closely and did quite a bit of sailing on them...something is VERY WRONG with this boat...your surveyor, unless he has looked at TONS of 105s is not going to discover what is wrong with this one.

it should not be that slow...under sail or power.. Even with a rookie like me it should easily do 6-8 with 12knts of wind...

You have been given lots of reasons to walk away, I would do so - there are plenty of 105s out there that will sail circles around this one and probably be a dream to live with.

Your call, but please don't let the time/survey/lust get in the way of the facts...this boat is not right.
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