Martin Brooking

Brilliant question Stephen and very clearly stated. In practice the class associations and MYA could introduce an accreditation process for sail makers. It doesn’t have to be complicated (like you I’m totally confident that our regular sail makers know exactly what they’re doing). So the sail makers themselves could devise something practical and reliable. That way accredited sail makers can supply accredited products. Some may argue that SMOD classes like ILCA (laser) have had instances of out-of-class sails and spars. But these tales are mostly apocryphal; and it usually only matters in big events (which like our sport, are usually subject to scrutineering).

Hi Andy, you probably know this already, but I’m still a keen and active dinghy sailor/racer. I still prefer Sunday club racing in my dinghy, so Sunday radio yachting events are out for me at present. Other family commitments (grandchildren) can restrict Saturday availability too. The above is bound to change over time.

Hi Brad, thanks for your reply. Yes, the behaviour of masts and rigs is a complex topic. My background in ship science and a lifetime in naval architecture does lead me more towards the science and engineering (and not always for the better!); and I totally agree there’s no substitute for hard-earned experience. Aluminium alloy is a complicated material to use and the hardening process complicates it further. As far as I know hardening doesn’t change the elasticity (Youngs modulus), but it can significantly increase the strength. So a hardened section doesn’t become stiffer, though it does become stronger. Any aircraft engineers out there might be able to help on that one - they’ll know quite a bit more about aluminium than a naval architect! There are several different manufacturing processes for tubes and mast sections, and production varies a lot. Manufacturing tolerances also lead to variations. The hardening process is also very variable and these together can lead to uncertain qualities of tube. In ship construction it’s standard for structural materials to be tested and certified against set standards such as classification society rules, so that the material properties are categorised and verified giving confidence in the materials used. Of course we don’t have that level of information for dinghy or model yacht components, so it’s a bit of a minefield. I’ll stop now. Sorry if I rambled a bit off the original topic. There’s a lot more to add about cold work hardening and other thoughts, but that won’t help anyone’s boat go faster! Time on the water is a much better idea.

Hi David, I’m afraid I don’t have enough knowledge of IOM history to know whether they had spreaders from the get-go, but the class rules list them as optional items, rather than mandatory. The B rig mast is quite a bit shorter, so the bending of the mast would be less than for an A rig. I would think the location of the mast in the hull is quite important - especially restricting any free movement at deck level, as this can make a big difference in how much the mast will bend between its base and the shroud points.

Great discussion! Sorry if this next point is a bit nerdy, but in selecting the right type of aluminium tubing for a mast, it’s worth bearing in mind that the tensile strength doesn’t have much bearing on the stiffness of the tube. Basically the tube stiffness depends mostly on two things: 1. The section dimensions (particularly the 2nd moment of area) and 2. The Young’s modulus of the material. I understand that different grades of aluminium have widely varying strengths, but surprisingly very similar values of Young’s modulus (about 70 GPa, give or take). In practice, this means two tubes of different alloys with identical sections (e.g. outside diameter and wall thickness) may have different strengths, but their stiffness will be pretty much the same. By the same token, you might select a very high grade of aluminium tube, with a thin wall thickness to save weight, but a lower grade alloy with the same outside diameter and thicker wall (to give equivalent strength) will actually be stiffer, because the section will have a larger 2nd moment of area (but of course it would be a little heavier). Again apologies if the above sounds a bit nerdy, but sometimes buying expensive materials doesn’t always have the outcome you’re hoping for! BG is absolutely right; if David’s B rig mast has a large section (diameter/wall thickness) and is well located in the boat, it may be adequately stiff without spreaders. It just needs to be tried out on the water.

Thank you Andy for persevering with this - and thank you to everyone who contributed so diligently. It seems we now have a definitive answer (though I sense another intense bankside discussion coming on). I still mostly sail dinghies; and usually they’re much bigger than a starting mark, so perhaps there’s less controversy. But for radio yachts the diameter of a mark might be almost half a boat length. So Andy’s original question is an important one and I’m relieved it’s been answered! We’ll still have claims from boats called OCS that they were not over the line, but at least we can now agree on which line is the correct one to use.

Hi David, Ah yes, I fully understand your points - I’ve been there too (some would say I still am!) and I’m no whiz with electronics either. But as I understand things, your current winch will turn at a certain rate (i.e. turns per second); and so a smaller drum will proportionally reduce the sheeting speed too. Have a fiddle with your transmitter - hopefully you’ll be pleasantly surprised. Having said all of the above, removing the winch drum is not usually necessary all that often, so maybe you could just carry out whatever maintenance is required, refit the drum and carry on sailing? M

Hi David, I guess the most obvious effect will be that you will reduce the range of the sheet travel roughly in proportion to the reduction in diameter. I believe the important diameter measurement is on the bearing surface of the drum, not the extreme diameter. You may be able to compensate for the reduced travel by using the adjustments available on your transmitter - and maybe you can try that out fairly easily before you remove the drum? A new winch might feel like a step too far, but there good are advantages to having a quicker winch. I have an RMG on my current boat and although it’s not the quickest it is more than adequate for club racing. The new Red Ant winches look interesting…. would be nice to hear from anyone who has one. M

Hi Eric, that’s a great summary. Thank you for replying so comprehensively. I’ve gained a much better understanding over the course of this thread. There is a well stocked angling store only a mile or two from my home. Armed with the above I’m going to check out what they have available. I’ll report back if I find a good looking product.

Thanks Stephen. I believe that's 4-strand, which is interesting. I think the lines I have are 8 strand (though really not sure). It will be interesting to compare and to see how your new rigging fares.

Good news Stephen! Can’t wait to see the boat on the water again. 80lb spectra … what is the brand and where did you source it? Hopefully if the boat’s ready on Saturday I can compare the cord you used with the heavier cord on my other boats.

Thank you John that’s very helpful. I see the rigging guide is fairly generic. As far as I know there are many different types of dyneema and many more different brands. I think it’s used by anglers too and I didn’t know if it was a good idea to explore their products. I was hoping someone might have some specific recommendations of readily available products. Thanks again M

I sail DF95s and IOMs and I’m hoping for some advice about choosing the best general cord for the lines. I do have a small supply of the standard thin dyneema that came with my 95 when I bought it in 2016 (yes, it’s an early boat). My wife’s 95 and my IOM were bought second hand and both have slightly heavier braided lines for sheets and standing rigging (on the 95 only). This line, though slightly thicker, runs well and has the benefit of being easier to tie - it seems a bit easier to adjust bowsies too. It’s also pretty robust and resists wear very well. Whereas the standard 95 line does fray quite easily and is a bit jerky with the bowsies. Sadly I don’t know what the heavier line is. Can anyone advise on a type/brand of good general purpose line please? And where is a good source? Thanks and regards to all

Hi Stephen, I haven’t used that supplier, but I have bought Vapex products - either from Mike Weston or from Amazon. For me, both of these have been very reliable. If you have Amazon Prime the obvious advantage is free rapid delivery (sometimes at a slightly higher price). Mike is very reliable and has the advantage of knowing DFs inside out! Martin

Hi Craig, Many thanks for your post and thoughts. I appreciate it because I'd really like to see more of this type of discussion on the forum. There's a lot of knowledge and experience out there and the forum is a great opportunity to share that. Is the photo you showed your latest boat? It looks fantastic and the finish is excellent. If you have time it would be great to see photos of your various builds and if possible a few thoughts on how and why you modified each successive boat and whether or not you thought the modifications were successful. There are a lot of different designs at my local club and it seems that as long as it's a metre long, pointy at both ends and displaces no less than 4kg, it gonna work ok! I've figured out that hull design, though important, is only a small part of what makes a successful IOM. The rig set-up makes a massive difference and of course a good skipper, who can adjust the boat (and himself) for the conditions of the day probably has the biggest impact on speed. I bought a Widget (early flat-deck design) as my first boat just under a year ago. I probably didn't give it enough time, but I became frustrated at how easily it would 'go down the mine' in gusty conditions when other boats were not. I wonder now, whether this trait was due to the flat-deck design having the rig set too high in the boat relative to similar boats with a 'vang well’, but most likely it was my lack of experience in setting the boat up properly. I bought a Lintel late last summer and have been really impressed with it's heavy wind performance against some pretty decent club competiton. My wife bought an Italiko from an elderly club member who was giving up radio yachting. Like the Lintel, this boat doesn't have the up-to-date lines of a modern narrow design, but in light to moderate conditions the Italiko has a very decent performance. I think you’re right about the risks of the bow design on my new build, but as you say the boat can easily be modified after it's built - and it's not such a big deal to make another hull if I need to! For me, this is an opportunity to indulge my interest in naval architecture and have a bit of fun. Your observations on hull design are really interesting and I'm looking forward to learning more about this in relation to IOMs as my experience progresses. I've been away for a few weeks and have made no progress at all since posting the photos. My next step is to buy some resin and cloth to get on to the next stage of the process. I can't wait to see it on the water and continue the learning process!

Haha! Thanks Ian, that's a nice compliment. Actually the photos are a bit like seeing something on eBay - they make the boat look good, but once you're close up you can see the imperfections! One of the advantages of using balsa strip is that most of the undulations in the hull can be removed by gentle sanding. The hull was quite un-fair when the planking was finished, but it surprised me how smooth it looks now. I'm pretty certain that it'll need some more filling/fairing before and after the glass cloth goes on. Do you have a build on the go at present?

A bit of an update... Sadly, recovering from a heavy cold and suffering from an eye infection I couldn't join my mates at the club for the Saturday morning racing in IOMs today. This was a huge disappointment for me as it was really windy and I love those conditions. But, no worries, I thought I'd give a brief summary of the meagre progress I've made since last time. The two partial bulkheads and foredeck are fitted and the aft well for the rudder post is partially fitted. Additionally I have cut openings in the hull skin for the rudder and fin. The next task is to fit and construct the fin box and surrounding structure to house the radio gear and shroud connection points. I'm feeling my way along slowly because I've not done this before and I'm aware that if I build things in the wrong order I could make difficulties. For example I think it's best to fit and glue the rudder tube inside the hull before gluing the top of the aft deck well, otherwise access for gluing will be difficult and I could risk a leaky joint. The boat shown in the photos weighs 275g, but of course there's no glass or resin used yet and I have yet to fit the aft deck and fin box etc. I'm guessing that's not especially light and would be interested to hear others views on this given the partial state of construction. The photo showing the hull profile has the rudder and fin loosely attached for a dry-fit/measuring session. They are "borrowed" from my old Widget and will be used in this hull. I'm slightly nervous about the bow, which I have deliberately designed with less rocker than most current designs. The aim is to achieve about a 1cm immersion of the forefoot in the final floating condition. This is to maximise hull length (the idea being to increase the maximum hull displacement speed which is roughly proportional to the square root of the hull length). I'm pretty sure it's an idea that's been tried before and probably discarded, but experimenting and finding out is part of the fun of building these things - right? Several people believe the idea is flawed because having an immersed fore-foot will work against tacking quickly. That's what we'll find out and is mainly why I'm a bit nervous! But on the other hand it also allowed me to make the bow quite full too, so I'm hoping this will help the boat resist nose diving in stronger winds... We will see.

This link is to Brad Gibsons’s excellent guide to a basic setting up process for an IOM. I understand it works well for pretty much any design of IOM. http://www.bgsailsanddesign.com/uploads/7/0/6/9/70698521/bg_sails_rig_tuning_iom.pdf It’s very well put together. For me it’s the sort of document I need to revisit frequently because it covers such a lot of information. One of the key points is getting the mast vertical as a starting point. This is tricky because when your boat’s on its stand, it’s difficult to see whether the design waterline is actually horizontal. I dealt with this by putting the stand on a smooth level floor and then moved the boat forwards and backwards to trim it until the bottom of the stern and forefoot were exactly the same height off the floor. I then checked the mast with a spirit level. Not perfect, but it provides a good baseline to work on.

Good point. I remember now that I had to replace the gooseneck bearings on my DF65 & DF95 after only a few weeks at Eastbourne. Again, not a particular problem in fresh water.

Happy New Year everyone! For what it's worth, my experience from a brief spell of membership at Eastbourne is that salt water (and it's only slightly salty on Eastbourne's lake) is a killer. In fresh water like we have at Hunts there is very little problem, provided you follow yachtsman's advice on keeping everything dry. My personal belief is that the the pesky Futaba-type connectors are especially prone to problems because they are so small and use tiny, thin connectors. They're very difficult to dry - especially so for those that push into the receiver (unless you're prepared to pull them off and reattach them regularly). I've not used Corrosion X, but I have worked a light grease into the open sides and ends of the connectors to help prevent water from reaching the small metal components. Recently I experience "battery failure" on my DF95. This was actually the connector on the battery having finally succumbed to corrosion. I think the battery is OK, but interestingly it's one I used at Eastbourne, so it has had some exposure to salt. I will replace the connector and give it a go (and protect the new connector). I would be interested to hear others views on how salt water compares to fresh when it comes to RC electrics.

Amazing work John - very impressive!

Thank you Richard. That’s really helpful.

Reading JT’s post, I absolutely agree on his points about weight. 100g is only 2.5% of the minimum IOM weight. It’s hardly worth worrying about for club racing. You can lose more time fluffing a tack, choosing the wrong end of the start or simply not setting the boat up well in the first instance. However my understanding from DavBS’ earlier posts is that the boat he was considering is 25% overweight. If I’ve got that right, that’s 1kg and maybe it really is a bit too much to contemplate for club racing.

Thank you for posting the photos Tom, you’re a prolific builder! I’d really like to know your current ideas for forming the kicker well, fin box and radio pot. My understanding is that the kicker well is needed to allow the rig to be placed lower in the hull, hence reduce heeling moment. The fin box is tricky because it has to exactly match the fin dimensions and needs careful construction to ensure accurate placement and no leaks. It also has to support 2.5kg of lead! The radio pot is convenient in use, but a bit of a nuisance to build. Do you use composites for these? My current build is held whilst I ponder these points. I’m sure you’ve grappled with them too at some point.

Tom, I absolutely support your idea, so yes please, do share photos and experiences of your builds. From my previous posts you'll know I have limited experience and haven't even completed one IOM yet. My build process is a bit stop-start due to not having a clear view ahead of the best process. I made lots of mistakes and would have benefitted reading more blogs. I expect my first mistake was deciding to use balsa (though it does have some advantages). Secondly I cut frames from 3mm ply, but this proved to be too hard to use pins to hold the planking in place. So I switched to foam board - much easier to work with. I now realise I could have used cedar and straps/rubber bands to hold the planks in place (balsa is not stiff enough to resist small indentations caused by straps). I'm currently a bit stuck, scratching my head on how to best arrange the internal bits for the radio gear, servos, battery and sheeting. I know I'll overcome all of these, but I'm sure you've been there too at some point, so your shared experience would be very helpful indeed.