Anchor Bridle

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AMCarter3
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Anchor Bridle

Post by AMCarter3 »

We always use a Bridle when anchoring. Our Mantus bridle has an exceptionally secure locking hook whcih, in my view, makes it one of THE best bridles I have ever seen or used. It certainly protects the windlass and adds a shock absorber to the anchor rode.

However, a friend of ours (engineering background), asked a question that I had never considered,,. "Does the load on the two bow cleats raise any concern the anchor load might bend the two bows inward and damage them?" Apparently she saw or read about a large catamaran where the bridle actually pulled so hard on the bow cleats that it bent the bows. My feeling / assumption is that the PDQ pontoon structure is extremely strong and would not incur any damage from using a bridle. What do you guys think about this?
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Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

duetto
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Re: Anchor Bridle

Post by duetto »

first, i hope to god i'm never out in a storm bad enough to bend the bows.

that aside i'd be interested to know what cat experienced the bends. most sail cats have a mast section running from hull to hull, so to bend the bow it most like would snap that. many power cats have solid deck with an i-beam at the end which should be pretty rigid.

we use a bridle all the time. i think it's 20' so the angle between the y is small. so the load would have to be off the chart which means the line forming the y would probably snap.

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Re: Anchor Bridle

Post by deising »

Mac, I could do some quick trig calculations to show the inward pull for any given tension on the main rode, but since I don't know the shear load that our bow cleats would withstand, that would not help. My intuition is that this would not ever be a problem in any scenario likely to happen.

If you put chain (essentially no stretch) across the cleats with little slack and then another chain at the midpoint to pull straight ahead with the boat sitting on dry land, you would put tremendous inward loads on the cleats and at some point break them, the fasteners, or fracture the fiberglass holding them, but I can't imagine the bows bending.
Duane Ising
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2006 PDQ MV 34 - hull 91, 75HP, 3-blade

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AMCarter3
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Re: Anchor Bridle

Post by AMCarter3 »

I heard a bit more in an email from my friend... She is a senior sailing instructor in San Juan Sailing's school and is out on the water now leading a week long course. She said the boat was a big sailcat -- a St Francis 50. Apparently, it did not "bend" the bows (I misunderstood), but the situation did put a serious strain on the bow deck fittings in the load direction. She said, "It’s been many years, but as I recall it caused something like stress cracks in the fiberglass at bows".

I agree with both of you. I can't imagine a scenario in the course of normal boating that would lead to bending or fracturing fiberglass at the bows on our boats. Especially since our Mantus bridle has 5/8" twisted nylon lines. I do think I let out more bridle line though. Normally, I have the bridle hook about 6' underwater (in our typical 15-40' anchoring depths. I think I'll extend it to 12' to 15'.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

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Re: Anchor Bridle

Post by Expatriate »

I have anchored out in the PDQ 34 for literally months at a time. My approach is to tie the snubber line to one bow, take it across to the other bow and put the chain hook there, then just make sure both sides are the same length. I do this for convenience, not for any particular structural reason. Each side of the snubber has about another 10 feet of line so that I can increase the length in really bad conditions.

Anyway, in a bad blow, the failures that I hear about are always snapped snubber lines, not broker cleats or fiberglass. I have a backup snubber line with chain hook all ready that I can use on the center cleat near the windlass. This is not ideal, but is fine for short term anchoring and not overnight. In any case, I never put the anchor load on the windlass.

Tim
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Re: Anchor Bridle

Post by thinwater »

Calculating the strnegth of the cleats is a matter of looking at the fixing boats and the backing plates. On the PDQs I've seen, the rope would probably break first, or at least not last long. They are stronger than anchoring loads require.

As for the bending force on the bows, it is really quite small compared to the forestay gull striker load on the sail versions. Trivial, in fact. Since the power boats use similar hulls and must have some manner of compression member near the bows, I'd worry about something else!

FWIW. I did a lot of anchor load testing on my PDQ 32/34 (it's in the book in my signature). The greatest rode tension you are likely to see is around 1000-1500 pounds at 60 knots, depending on the model and assuming you are not in breakers.

And a narrow little bridle angle like that does increase the load on the bridle, weakening it. Really, the legs should be at least the beam width in length. The boat will also yaw less, further reducing the rode tension. Yeah, a really short bridle like that could overstress things. Look at the angle on the Y-splice! And you are reducing the rope available shock absorption. Let more out! The apex angle should be less than 60 degrees.
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Re: Anchor Bridle

Post by AMCarter3 »

Excellent advice. This has been a good discussion. Thanks.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

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Re: Anchor Bridle

Post by Expatriate »

One final note on all of this. I agree that each leg of the bridle should be about equal to the beam of the boat. It gives an almost perfect angle.

In the past, when the wind totally died at night, my chain hook would come off the chain. Extra chain between the bow roller and the hook usually fixes this, but not always. If it drops to the bottom and drags around, it will come off eventually.

I was advised by Dick Tuschick to try the Mantus chain hook. I love it. If it has a week link, it would be the plastic/rubber part, but even without that the shape alone will help contain the chain. It is very robust and totally worth the cost.

Tim

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AMCarter3
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Re: Anchor Bridle

Post by AMCarter3 »

I agree, Tim. I have the Mantus bridle. It is outstanding, Note that our boat is in a charter business - different people charter our boat Nearly every week from April thru mid Oct. I have not seen a single issue with the bridle or its plastic latch that secures the hook to the chain. I am sold on this bridle.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98; twin 100 HP Yanmars
Home Port: Bellingham WA 98229
Member of San Juan Sailing & Yachting Charter Fleet: http://sanjuansailing.com/charter-detai ... .php?id=35

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Re: Anchor Bridle

Post by duetto »

we have a chain/rope rode. 60' of chain. almost always let out more than the chain. regardless, we've always done a rolling hitch using the pigtail of the y splice.
john & diane cummings
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Re: Anchor Bridle

Post by bjgin »

I had the same concerns so I mounted 10" cleats 2' above the waterline and about 2' from the front of the bow with 1' thick large plywood backing plates. Also backed by 1/4" 8 x 6 aluminum plates. This gave the anchor rode a low angle of attack. When not in use I secure the apron over the bow rail. Works quite well.
BJ and Ginny Patterson
2004 PDQ MV34, #40, 110 Engines
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The Villages, FL

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