Rocker stoppers

By Mike

Rocker stoppers are intended to reduce the rocking effect induced in a small boat by the action of choppy waters. I obtained a set of 6 in mid June 07 and this is the results of the first test:

Let me start with the conclusion - rocker stoppers really do work .... but they don't stop you rocking. Read on and all will become clear

I think my Warrior 165 is a very stable fishing platform but after a couple of people I took out complained of queasiness, I thought I would try and obtain some rocker stoppers. They come from the same stable as the original Doelfins that many sports boat users fit to their outboards to stop the boat porpoising at speed. In the USA they are distributed by Davis Marine but it seems Unipart have got the contract to distribute them over here - their part number is 181210 and most chandlery shops can order them for you

These images are copied from the Davis Marine website and show what the rocker stoppers look like and how they should be deployed

The website and literature suggested boats up to 26ft would need a string of 3 each side and boats bigger than this would need proportionately more. Since my boat is only 16ft, I wondered whether I might get away with just 2 each side (and this proved to be the case). At between 6.50 and 9 each it obviously makes a difference in cost terms how many you need.

The only other costly item is the weight that you need each side to keep the string of rockerstoppers vertical in a strong current. Their website suggests some very neat mushroom anchors but these seem to be unavailable in the UK - at least in the small size that's needed for a small boat - (8 to 10lb ). One of my local chandlery shops sells a folding grapnel anchor for 9 that weighs 3.2kg. For me that was near enough the weight and would also mean that I would have TWO spare easily carried anchors on the boat in case my normal 5kg Bruce anchor didn't hold if I got caught out in bad weather.

Stainless steel clips and accessories seem suddenly to have dropped in price in the shops recently so the rocker stopper strings are now dotted with several caribiner type miniature clips. Remember the strings are not carrying much weight so the fastenings don't need to be over the top - more on this later. One of the s/s caribiners tied to the bottom of the string clips to a plastic tie in the eye of the grapnel anchor. Another is at a point 94 inches higher up the string. Why so precise you may ask? Well I measured the distance from the support point to the rotating prop as 109 inches, so if I set off in a hurry and forgot to uplift my rocker stoppers, they would just fail to crunch into the prop. There is a flaw in this argument though that I will have to address soon. If I set off in a hurry, the force generated is quite likely to snap the other plastic tie used for the upper caribiner - in which case the grapnels will hit the prop anyway.
In the first trials - in pretty rough conditions the slightly feeble plastic tie I was using at the gunnel rail, gave way simply under the force generated by 2 rocker stoppers. A meatier tie seems to have cured this but it does of course raise the question about how much force will be acting on the gunnel rail. It is surprisingly easy to find out and you will already have the tools to do it - your fish spring balance. Simply insert this between the top caribiner and the plastic tie on the gunnel rail and watch the dial as the boat rocks and the rocker stoppers do their work. In my case it seemed to peak out at about 20kg - I know this sounds a lot but I was happy that it was unlikely to weaken the joint between gunnel rail and fibreglass. If you are really worried about this you can of course tie them off to a proper cleat, but in the case of the Warrior the only suitable pair is at the stern, and experiments showed this position to be less effective in countering the rocking action. The stern cleats did however come in useful, because I made the strings about 3 ft longer than necessary and my rule is that before putting them out I put the loop at the top end over the stern cleat. That way if I drop them - or the plastic tie at the gunnel breaks, I'm not going to have 27 worth of gear torpedoing to the sea bed..
I have one final safety feature that I built in - a red cord that I loop round the throttle lever as a reminder that the rockerstoppers are out. Hopefully this will prevent me shooting off to the next mark prematurely.

So to the crunch question - do they work? And the answer is a qualified 'yes'. Don't however think for a moment that chucking 2 or 3 of these off the side of your boat is going to make your Warrior behave like an oil exploration platform - you will still rock. But you won't oscillate and the difference is noticeable. We've all been there, where a series of short chop waves have started the boat rolling and each one seems to reinforce the last so you have to sit down pretty quickly before you go stumbling into the gunnel.
This is drastically reduced by rockerstoppers - and you can see why - as one gunnel tries to rock upwards the string of cone shaped disks move so much water that you can see it surface in a gently boiling patch a couple of seconds later. And this is what creates the damping effect. I was worried that if the upward moving gunnel was prevented from so doing, wouldn't that mean it was likely to let a wave pour over the top? I watched this very carefully and the chop was pretty big probably about 3 ft trough to peak - at no time did there look to be any danger of the water coming over.

I've talked about how to fasten the string to the boat and to the anchors/weights, but how do you make up the business part of the device. Each rocker stopper comes with a 10mm hole in the crown, so it's important to use a 10mm diameter length of rope. This is because to locate each one in the right place you use a pair of simple half hitches one beneath the crown and one above it. The rocker stoppers should be spaced at 18 inch intervals. For the first experiments I used just two rocker stoppers on each string - and they worked. You can see the effect in the video which was shot before I upgraded each string to 3 units. I think on a small boat like a Warrior 165 you can get away with using just 2 either side. But my advice would be to buy 3 and here's why.

The second experiment was to see if rocker stoppers slung from the bow roller would slow drift on a windy day. And the answer is yes and no. Yes they will but only if you clip both strings of 3 together. The instructions advise using a smaller weight for this purpose and I clipped in a 12 oz lead and tossed one set of 3 out of the front hatch (after looping the end over the bow cleat). The effect was minimal, and the boat assumed its usual side-on aspect to the wind and stayed like that. I found this pretty deflating then realised that I could quickly clip the other string of 3 to the loop that was round the bow cleat. Wow - what a difference - within 30 seconds the bow had come round and all 6 rocker stoppers were nicely dug in just below the surface. All of a sudden the wind was gone - well it wasn't but of course now the cuddy was doing the job it was intended for ..... very pleasant. There are however two disadvantages - these would apply to any drogue system - firstly of course you end up fishing towards the bow rather than off the side or rear as you would on a normal drift, and secondly if you are using all your rocker stoppers out the front, you can't use any to reduce lateral rocking. Mind you if your bow is pointed into the waves, lateral rocking is probably considerably reduced anyway.

Drift speed with the chain of 6 rocker stoppers hung on the bow did not seem to be much affected. Watching the GPS it seemed to be about 1.3 knots without them and possibly 1knot with them .... but it may have been simply down to changing state of the tide.

The product is imported and distributed by Unipart and their product number is 181210. So in conclusion Rocker stoppers seem to do what they say on the tin, and for a price of about 50 you can kit yourself out with an abundnace of them including a couple of spare anchors and an effective drogue system. If you are prepared to make your own weights and cut your purchase down to just 4 units, you can probably get a working system for less than 30

Click here to see a video of rockerstoppers in action


Return to Other Bits index