Gull / Dolphin Striker Tension

[ausnp84]

Happy Boxing day folks!

Any general advice for gull striker and dolphin striker (supports the sprit) tension?

We have a Punch 9m catamaran that’s recently been re-rigged, and after the first few sails I’m thinking things could probably do with a tighten up.

The gull striker has the usual A-frame in the middle and a single turnbuckle, and grabbing it with a full hand and giving it a yank, I can deflect it approx 1” currently.

Same for the dolphin striker. About 1” deflection from straight.

I know the side stays should be relatively taut, but how tight is too tight for the strikers? 7mm wire, 5m beam.

N

[ausnp84]

Photo of the current setup.

N

[tamicatana]

They should be prebent to whatever setting achieves a straight beam when the headsail is rigged.

As an example, bc each boat is different, my fwd x-beam has a 2” prebend. It lies straight once the forestay and jib are rigged.

[Tupaia]

Are you afloat again, new boat? Punch's are nice light cats.

My A frame wires are bar tight, 12mm and wide beam, but as tamicatana says this is boat dependant. There is a good chance it is too loose if it changes because of furler halyard tension or when the mainsail is up. Is the rest of the rig, diamonds, mast pre-bend and shrouds adjusted correctly?

Not sure what you mean by dolphin striker your boat appears to have water stays. These are tensioned by the spinnaker/screecher halyard and stiffness will be governed by the top mast, supported by running backstays, mainsail leech tension or the topping lift. The weak points will be the hull attachments. These can pass completely through the bows, tied to the crash bulkheads or with simple backing pads. None of this should affect the gull striker tension, unless the mast is bending and relieving the forestay tension. The sprit may put backwards pressure on the forward beam that may have a compression strut to transfer the loads back to the apron.

[ausnp84]

Originally Posted by tamicatana

They should be prebent to whatever setting achieves a straight beam when the headsail is rigged.

As an example, bc each boat is different, my fwd x-beam has a 2” prebend. It lies straight once the forestay and jib are rigged.

Thanks, but as it appears the cross beam is a 4m length of ally mast profile, it doesn’t have any pre-bend.

I guess the thing will be to keep tightening the martingale turnbuckle until the crossbeam just begins to bend.. I wasn’t sure though if doing that could risk tearing out a fitting or damaging the crossbeam.

N

[tamicatana]

Originally Posted by ausnp84

Thanks, but as it appears the cross beam is a 4m length of ally mast profile, it doesn’t have any pre-bend.

I guess the thing will be to keep tightening the martingale turnbuckle until the crossbeam just begins to bend.. I wasn’t sure though if doing that could risk tearing out a fitting or damaging the crossbeam.

N

None of this has to do with the martingales. They hold against a bowsprit and the headsail it carries.

The A-like strut at the center of your forward X-beam, with its tensioning cable, is known as a gull striker if points upwards, and works against the upward loads induced by the forestay. A similar rig that points downward and is usually on a main X-beam to resist mast downward forces is known as a dolphin striker.

Prebend is induced before the forestay is attached to the beam, by tensioning the gull striker turnbuckle. I have a mast section as my fwd X-beam, boat is a Catana 40S, my pb is about 2 inches.

Then rig the forestay and tension it and the rig. Once all that is done, the beam should then be straight. That is how you know your prebend is correct. Depending on the boat spec; some designs vary. That is to say, you may still see a bit of prebend but as your mainsheet tension comes on, it will flatten.

[ausnp84]

Originally Posted by Tupaia

Are you afloat again, new boat? Punch's are nice light cats.

My A frame wires are bar tight, 12mm and wide beam, but as tamicatana says this is boat dependant. There is a good chance it is too loose if it changes because of furler halyard tension or when the mainsail is up. Is the rest of the rig, diamonds, mast pre-bend and shrouds adjusted correctly?

Not sure what you mean by dolphin striker your boat appears to have water stays. These are tensioned by the spinnaker/screecher halyard and stiffness will be governed by the top mast, supported by running backstays, mainsail leech tension or the topping lift. The weak points will be the hull attachments. These can pass completely through the bows, tied to the crash bulkheads or with simple backing pads. None of this should affect the gull striker tension, unless the mast is bending and relieving the forestay tension. The sprit may put backwards pressure on the forward beam that may have a compression strut to transfer the loads back to the apron.

Howdy - I think you’re referring to my last cat that was written off and this Punch is indeed the new boat.

Thanks for the heads up on your a-frame wire tension; the rest of our rig is setup and tuned per our rigger’s instructions - he was just a bit vague about the a-frame / crossbeam wire (“tight, but not too tight”).

So the water stays pass through the hulls with an eye bolt on one side and nut on the other. They then connect to the end of the sprit to counteract the load placed on it by the permanently connected furler (it has that furler with a dacron sail, rather than an occasionally connected spin). It sounds like as it’s permanently connected, those water stays need to be tightened up as well to give proper tension to the sprit...

N

[ausnp84]

Originally Posted by tamicatana

None of this has to do with the martingales. They hold against a bowsprit and the headsail it carries.

The A-like strut at the center of your forward X-beam, with its tensioning cable, is known as a gull striker if points upwards, and works against the upward loads induced by the forestay. A similar rig that points downward and is usually on a main X-beam to resist mast downward forces is known as a dolphin striker.

Prebend is induced before the forestay is attached to the beam, by tensioning the gull striker turnbuckle. I have a mast section as my fwd X-beam, boat is a Catana 40S, my pb is about 2 inches.

Then rig the forestay and tension it and the rig. Once all that is done, the beam should then be straight. That is how you know your prebend is correct. Depending on the boat spec; some designs vary. That is to say, you may still see a bit of prebend but as your mainsheet tension comes on, it will flatten.

That makes a lot of sense - thanks. I think martingale got thrown in as a term somewhere else and had me confused.

At this stage the whole rig is tensioned and the cross beam is straight, however there is still play in the a-frame tensioning wire. I’m going to wind it up tomorrow until pre-bend just starts, and then monitor it as we continue test sailing to make sure it’s tight enough.

Thanks again for the advice.

N

[Tupaia]

Originally Posted by ausnp84

So the water stays pass through the hulls with an eye bolt on one side and nut on the other. They then connect to the end of the sprit to counteract the load placed on it by the permanently connected furler (it has that furler with a dacron sail, rather than an occasionally connected spin). It sounds like as it’s permanently connected, those water stays need to be tightened up as well to give proper tension to the sprit...

N

Through bolts for water stays are an excellent setup and the anchorage points are easy to monitor.


Is the outer forestay attached to the sprit by a fixed wire?


If the roller is a fixed length wire then you will need some way of tensioning and locking off the water stays. This would be very unusual.



Is there a universal pivot at the inner end of the sprit?


If it is rigidly attached to the X-beam then there is likely to be fatigue issues resulting from the sprit twisting the x-beam. Again this would be very unusual.



The reason I ask is that normally the water stays are a fixed length and the forestay is a torque rope that is tensioned by the halyard or a rigid foil with a wire halyard at the top both would be adjusted at the mast.



Assuming the sprit IS pivoted then the A-frame tension / adjustment will not be affected unless it is tensioned to the point where the pressure on the inner forestay is relieved.

[Matt Johnson]

If you guys look closely at the photo, there is a dolphin striker right in front of the anchor. It's a short one and easy to miss.

[ausnp84]

Originally Posted by Matt Johnson

If you guys look closely at the photo, there is a dolphin striker right in front of the anchor. It's a short one and easy to miss.

Spot on - it’s only about 5” long and the wire that tensions it is taut to the point I thought it was going to break the welds...

(BTW - are you the same Matt J who’s building the cat, as in MJ Sailing? If so, loving the channel - you guys are doing an awesome job).

N

[ausnp84]

Originally Posted by Tupaia

Through bolts for water stays are an excellent setup and the anchorage points are easy to monitor.

Is the outer forestay attached to the sprit by a fixed wire?

If the roller is a fixed length wire then you will need some way of tensioning and locking off the water stays. This would be very unusual.

Is there a universal pivot at the inner end of the sprit?

If it is rigidly attached to the X-beam then there is likely to be fatigue issues resulting from the sprit twisting the x-beam. Again this would be very unusual.

The reason I ask is that normally the water stays are a fixed length and the forestay is a torque rope that is tensioned by the halyard or a rigid foil with a wire halyard at the top both would be adjusted at the mast.

Assuming the sprit IS pivoted then the A-frame tension / adjustment will not be affected unless it is tensioned to the point where the pressure on the inner forestay is relieved.

Ok - hopefully these pics come through at a decent enough quality and answers to your q’s below:

Yes - the outer forestay is connected to the sprit by a fixed wire / roller furler.

The water stays are a single wire that pass through a ring on the bottom of the sprit, and then have a single turnbuckle for tensioning.

No universal pivot for the sprit - it’s bolted to the longitudinal walkway (that bisects the trampoline) AND it’s also riveted to the underside of the crossbeam. In theory, with no water stays or no outer forestay wire, the sprit would just sit there and not do a lot (it’s only about 2ft long I might add).

It’s almost like they decided they needed a bit of extra length for another headsail, so they added a mini-sprit, attached a furler on top and the water stays beneath to hold it all together...

N

[meirriba]

Originally Posted by ausnp84

Happy Boxing day folks!

Any general advice for gull striker and dolphin striker (supports the sprit) tension?

We have a Punch 9m catamaran that’s recently been re-rigged, and after the first few sails I’m thinking things could probably do with a tighten up.

The gull striker has the usual A-frame in the middle and a single turnbuckle, and grabbing it with a full hand and giving it a yank, I can deflect it approx 1” currently.

Same for the dolphin striker. About 1” deflection from straight.

I know the side stays should be relatively taut, but how tight is too tight for the strikers? 7mm wire, 5m beam.

N

I believe there is a misuse of terms that confuses us and gives you confusing answers in return.
On a catamaran:
Dolphin striker - keeps tension on the front crossbar.
Martingale (or bob stays) - keeps tension on the bowsprit.

Dolphin striker should be tensioned to give slight upward curve to the crossbar.
Martingale wires - just hand-tight. The sail gives it upward tension, and the stays will keep the bowsprit from rising up.

[ausnp84]

Originally Posted by meirriba

I believe there is a misuse of terms that confuses us and gives you confusing answers in return.
On a catamaran:
Dolphin striker - keeps tension on the front crossbar.
Martingale (or bob stays) - keeps tension on the bowsprit.

Dolphin striker should be tensioned to give slight upward curve to the crossbar.
Martingale wires - just hand-tight. The sail gives it upward tension, and the stays will keep the bowsprit from rising up.

Sure thing - unfortunately I can’t edit the original post. To avoid any confusion, the stay tension we’re talking about is:

1.) The stay that connects at either side on top of the crossbeam, and has the A-frame in the middle.

2.) The stay that runs between the the forward, lower bows and connects to the forward lower of the sprit. I understand these are called martingales / bob stays / water stays.

N

[tamicatana]

[QUOTE[/I]=ausnp84;3544674]Sure thing - unfortunately I can’t edit the original post. To avoid any confusion, the stay tension we’re talking about is:

1.) The stay that connects at either side on top of the crossbeam, and has the A-frame in the middle. =Gull striker if pointed upward, and dolphin striker if pointed down. You have a gull striker on your fwd xbeam and a dolphin striker on your sprit.

2.) The stay that runs between the the forward, lower bows and connects to the forward lower of the sprit. I understand these are called martingales / bob stays / water stays. Yes

N[/QUOTE]