Weed hatch anti cavitation/baffle plate

[Markinaboat]

Some boats have em, others don't. I've had two nb's with an anti-cavitation plate at the bottom of the weed hatch and three without. I've experienced no difference with noise/banging, power loss, turbulent wash (outside of the norm) etc.

 

Our current (new to us) boat has one permanently attached to the hatch cover. It makes it virtually impossible to lift/tilt back to access the prop. The fact that the top is 8mm steel with the cavitation/baffle plate bring 5mm and the interconnecting 2 X steel snake iron joining pieces makes it ridiculously heavy too.

 

So, what are your views on this as we can have it (anti cavitation/baffle plate) cut off tomorrow so I can access the prop when the inevitable southern GU blankets, sari's and mattress attach themselves to our 25" prop!

 

I should add that the hatch seal and clamping down methods are top notch.

 

Thanks in advance

 

Mark

[blackrose]

Cut it off with an angle grinder if you don't want it, but keep the baffle plate just in case things get worse and you need to get it welded back on. Before taking the boat out I'd run the engine in gear and check water isn't leaking in. The baffle plate defects a lot of water pressure, some of which which might otherwise find its way past the weed hatch seals.

[Markinaboat]

Thanks. That's the plan although if enough room, he may weld it back on but much higher up, maybe 3-4" below the hatch cover.

 

I would most definitely run it at full revs tied up for a good 10 mins before I cast off. The seal is a nice thick solid rubber affair, not the thin sticky-backed stuff.

[OldGoat]

Cut it off with an angle grinder if you don't want it, but keep the baffle plate just in case things get worse and you need to get it welded back on. Before taking the boat out I'd run the engine in gear and check water isn't leaking in. The baffle plate defects a lot of water pressure, some of which which might otherwise find its way past the weed hatch seals.

Seconded. I think the baffle -

Makes for quieter running

makes the propulsion more efficient

 

Mine is a pain to lift, but the hull builder provided two large handles, making it possible to lift....

I stand astride the hole, lift and tip it forward, take a rest, change position and lift it topside.

 

But then if you're determined......

After all they were designed for a reason.

[DHutch]

Or, clamping arrangments aside, put the whole lot to one side and get a piece of 4/6mm plate to make a new top.

We have a plate on ours, but the top and plate are no where near 8mm thick and its manageable enough for the once a year or so we need it.

That said, theres only one way to find out and if it doesnt work how it is and an easy fixed does the job for you....

 

 

Where does the water level sit with regard to the uxter plate and or the top of the weed hatch?

 

Echo the comments about it increasing the reliance on the seal.

 

 

Daniel

[ditchcrawler]

Can you just try it by clamping it on up side down with the cavitation plate up in the air. I have seen that done when trying to trace a vibration. (it was the cause)

[bizzard]

If the plate is held down by a centre turn screw, as most are, then it should have an X shaped reinforcing web welded to its top surface with a socket in the middle to take the holding down turn screw. Without the X reinforcing web a plate of 6mm or less thickness will warp (cup) under the screw pressure and so compromise (lessen the effective gasket sealing area and make it liable to leak.

[blackrose]

Can you just try it by clamping it on up side down with the cavitation plate up in the air. I have seen that done when trying to trace a vibration. (it was the cause)

That's not a bad idea. Or if it won't fit upside down, just clamp a sheet of steel over the hatch with small clamps.

 

http://www.amazon.co.uk/gp/aw/d/B0018A8XAA/ref=mp_s_a_1_3?qid=1452714375&sr=1-3π=SX200_QL40&keywords=Mini+clamps&dpPl=1&dpID=41VCEBYEbAL&ref=plSrch

[Sea Dog]

I don't have one on mine and, like you found on some other boats, I suffer no ill effects. I considered modifying it because it seems like a sensible thing to have, but I wouldn't be able to remove the assembly if I did as it's under the steerer's step and there'd be insufficient head room. Now I'm perfectly content that I don't need it.

 

Simon Piper built my boat, and he (like his dad before him) has built a few. Perhaps the need for one depends on the hull hydrodynamics?

 

I'd replace it with a plate so it's easy to change as you go through trials, then you'll be able to carry out a most objective assessment. It shouldn't be hard or costly to manufacture.

 

Failing that, chop it off and retain for replacement should you need it when you assess how she is without it.

 

Good luck!

[Markinaboat]

No flap on the deck (which I don't want). Access from behind steerers step. Underside of deck is too close to the plate to lift fully so can't invert to test. Has to be lifted and tilted back but too tight a clearance hence reducing distance from baffle to top plate. It does have the centre recessed screw down fixing with a cross bar that fits around the sides of the box.

 

The best solution would be to have the box built up to deck level with a hinged flap on deck (aka Tim Tyler hulls) but a lot of money as difficult to access for welding etc without ripping out all of he internal joinery.

 

Advised that due to the 25" prop (driven by a Gardner 3L2) there would be no noticeable difference to noise/buffeting or propulsion. Boatyard reckoned small props may cause an issue.

 

Thanks for all your replies.

[FadeToScarlet]

Chop the baffle plate off, but have a handle welded between the vertical bits. Then, you remove the lid, then remove the baffle plate separately.

[Markinaboat]

Chop the baffle plate off, but have a handle welded between the vertical bits. Then, you remove the lid, then remove the baffle plate separately.

That would need supports welded at the bottom of the box and it could vibrate up and down. It can't be pressed down by steel uprights attached to the top plate as that could prevent the top plate being tightened down sufficiently as the rubber seal compresses over time. If that makes sense!

[WotEver]

That would need supports welded at the bottom of the box and it could vibrate up and down. It can't be pressed down by steel uprights attached to the top plate as that could prevent the top plate being tightened down sufficiently as the rubber seal compresses over time. If that makes sense!

Large (or two small) rubber block glued to the underside of the top plate?

 

I realise you'd still require supports welded at the bottom of the well, so certainly not as easy as just cutting it off.

[FadeToScarlet]

That would need supports welded at the bottom of the box and it could vibrate up and down. It can't be pressed down by steel uprights attached to the top plate as that could prevent the top plate being tightened down sufficiently as the rubber seal compresses over time. If that makes sense!

Are there no protrusions around the outside of the weedhatch at all? Of the ones I've seen, the trunking upwards is wider than the hole in the Uxter plate, giving a lip for the baffle plate to sit on.

[Markinaboat]

Are there no protrusions around the outside of the weedhatch at all? Of the ones I've seen, the trunking upwards is wider than the hole in the Uxter plate, giving a lip for the baffle plate to sit on.

Unfortunately not. That would've made things much simpler!

Large (or two small) rubber block glued to the underside of the top plate?

I realise you'd still require supports welded at the bottom of the well, so certainly not as easy as just cutting it off.

Good idea

[FadeToScarlet]

It sounds like you've got a fairly deep draught, have you tried stopping in a bridgehole or lock and clearing the blade with a cabin shaft?

 

I find it so much quicker, easier, and drier on this (weedhatch-less) boat than having to duck under the counter and shift a weedhatch lid and baffle plate dripping silt everywhere.

[Markinaboat]

It sounds like you've got a fairly deep draught, have you tried stopping in a bridgehole or lock and clearing the blade with a cabin shaft?

I find it so much quicker, easier, and drier on this (weedhatch-less) boat than having to duck under the counter and shift a weedhatch lid and baffle plate dripping silt everywhere.

I used to do that with Marcellus (the big real one) but my back/hips aren't being so kind to me these days. I still use this method occasionally but difficult yo gphit the right spot on current boat. Approx 2'9" draft. Hopefully the mods tomorrow will make it doable for me.

[DHutch]

Are there no protrusions around the outside of the weedhatch at all? Of the ones I've seen, the trunking upwards is wider than the hole in the Uxter plate, giving a lip for the baffle plate to sit on.

Ours is the same, if you did what you suggest, the baffle plate would just fall thought onto the prop and into the cut!

 

 

Daniel

[Sea Dog]

The best solution would be to have the box built up to deck level with a hinged flap on deck (aka Tim Tyler hulls) but a lot of money as difficult to access for welding etc without ripping out all of he internal joinery.

 

Plus you may find your arms are no longer long enough to reach down the hole effectively. There's not much that's not a compromise on a narrow boat!

[Top cat]

When we bought Grace she didn't have an anti cavitation plate and we were plagued with sticks getting janned in the weed hatch. So we had a plate fitted and immediately notced. Less prop noise, smoother prop wash, better stopping and less stuff getting caught on the prop and when it did a much better chance of a chuck back clearing it.

 

Top Cat

[KroSha]

Purely anecdotal, but we had a cavitation plate on our Springer. A couple of close friends didn't. We had significantly less problems with junk getting caught around the prop over the same sections of the cut. In fact, we went a good 3 years without getting anything caught that needed us to go down the hatch.

[nebulae]

On open water at full speed,the vibration of the cavitation plate was frightening .Bottom plate(5mm) replaced with a 10mm plate,no more problems.Weed hatch now needs arms like Popeye but quiet at speed(6 knots according to G.P.S.)

[Markinaboat]

Sorted by the brilliant Steve at Bullsbridge Dock in Hayes. Fabricated a new one but around 1" shorter (so cavitation plate is 1" up into the hatch) and substituting a 10 mm top with 5 mm and the 6 mm cav plate with a 4 mm one.

 

Now I can tilt, lift and slide away. As be blacked it, we put the old top plate on only and I can tell you without a cavitation plate, it was banging every so often, tiller vibration and I could sware the steering wasn't as precise but that could have been the wind. Will know for sure tomorrow when I put the new one in.

Edited January 14, 2016 by Markinaboat

[bizzard]

Sorted by the brilliant Steve at Bullsbridge Dock in Hayes. Fabricated a new one but around 1" shorter (so cavitation plate is 1" up into the hatch) and substituting a 10 mm top with 5 mm and the 6 mm cav plate with a 4 mm one.

 

Now I can tilt, lift and slide away. As be blacked it, we put the old top plate on only and I can tell you without a cavitation plate, it was banging every so often, tiller vibration and I could sware the steering wasn't as precise but that could have been the wind. Will know for sure tomorrow when I put the new one in.

See post 7

[Markinaboat]

If the plate is held down by a centre turn screw, as most are, then it should have an X shaped reinforcing web welded to its top surface with a socket in the middle to take the holding down turn screw. Without the X reinforcing web a plate of 6mm or less thickness will warp (cup) under the screw pressure and so compromise (lessen the effective gasket sealing area and make it liable to leak.

I've had three boats where the top plate is 6mm or less without web bracing to the baffle plate. All had a centre screw-down for the side clamps. Have always used thick rubber and have never had a leak yet? Fingers crossed!

 

I should add that the top flange of the box is around 1.5" wide.

Edited January 14, 2016 by Markinaboat