Hi Niel,
Presently the mark II hull basically only has 10mm added to the top end to end so increasing the rocker is possible. Certainly our full size experience would say get the transom out of the water if it isn’t a planing hull. How much do you think is the go? It would seem possible to raise both the bow and the stern by the 10mm added to the deck level. Maybe split the difference and go for 5mm? We haven’t cut balsa yet.
Regards
Peter & Clare
Hi Peter and Clare - I float my hulls so that the stern end is on the waterline, just kissing the water surface without depressing below. The bow and the stern on my Tanto design are on the waterline and the bow digs in as soon as she starts to accelerate (like all Footies do). I believe that it was Gary who recommended, on this thread or elsewhere, floating the bow high at rest so that when the boat gets some way on her she levels out and sails on her waterline. I haven’t tried that concept yet.
I would probably go with 10mm. But before building the hull the rest of the way up I would do a float test as I described in the adjacent “Papaya Sideways” thread. Only you guys would be looking for the displacement numbers as well as the new center of bouyancy. You’ll need to have some weights and a scale handy. Once you have the hull floating more or less where you would like it you can use coins to add a bit of weight to the bow or stern to see how the hull reacts and balances out.
I noticed that HOP2IT has a sharp bow. You may want some of that bow below the waterline or you may try balancing the boat bow up to some degree as I mentioned above. In the float test you may find that you need more immersed hull to make the desired overall displacement with the stern just kissing the waterline. Then again you may need less. If you need 50(+) grams less then I would reduce the new rocker a ways back towards that of your current version. On Tanto I can float her at 540 grams, but she seems to like 510 grams just fine. Floating a bit high on her lines static is fine because Footies, as displacement craft, dig a trough as they get moving. You may have noticed that HOP2IT sinks a bit as she drives through the water.
Tanto is a diagonal placement boat. As such her waterline is longer than your HOP2IT but she is probably narrower. The rocker measurement (maximum hull depth measured from the waterline) is 39mm +/- on the three hulls I’ve built so far. This might be helpful to give you a ballpark figure. You might want to try a mark 3 hull with diagonal box placement. Look up my article on the Footy Website for more info.
Hi All,
Thanks to all for suggestions re improvements in our design. The outcome is that we cut balsa today for the HOP2IT mark 2. In the end we decided to go with a diagonally placed design but not tilted as well. This gave a 320mm OAL and a DB of 100mm. The height of the hull has been increased by 10mm as suggested and the rocker increased particularly at the stern. Theoretically the transom should be out of the water at the design displacement of 400g. The weight of the hull as pictured is 13.5g compared to our original boat’s 9.9g at the same point. It is a larger hull so the percentage increase is about right.
Regards
Peter & Clare
Guys, thats a nice looking hull!
Yup! Looks very much like a Cobra 3. Great minds and all that…
Scott
Hi Niel & Scott,
Thanks for the positive feedback. It looks like we might be heading in the right direction. We have not done much over the last couple of days but the 3/4oz cloth is applied to the outside of the hull and there is a coat of epoxy on the inside. The current weight is now 26g. This compares well with the original hull at the same stage.
Regards
Peter & Clare
Not much progress has occurred as we have been playing around with HOP2IT mark one and trying to determine if its boat speed is good bad or otherwise.
For such a small increase in length Mark 2 certainly makes mark 1 look small. We annealed a piece of 1/8 K&S brass tubing and formed a turn around for the main sheets for going through the deck. Even though it will have more surface area contact between the tube and the kevlar thread it has to have less sticksion than the present arrangement we have using a piece of NyRod inner. We have also gone with a hatch for version 2 instead of the electrical tape. There was a Kiwi site where we read that apparently tape is better for keeping water out but wasting tape every time you sail doesn’t seem right.
Interestingly we actually met some other local model sailors on the weekend (they didn’t have their boats with them at the time). Obviously it was most unlikely that they would be sailing (or have heard of) footies. They all sail another DIY model called a WeeNip. We checked the plans and at a length of 700mm they are huge compared to the footy. With a theoretical hull speed of 50% more than a footy it doesn’t appear to be much point sailing a footy with them. Unfortunate as you all seem to infer that fleet sailing is the best way to go.
Regards
Peter & Clare
Peter and Clare
As more learned pens than mine have said - lovely hull you have evolved to:D
I’m not an expert in this (or any) field, but have an increasing leaning towards “blunt” bows for a footy, as well as considerable area in the first third of the boat (which you have). I feel that in the downwind posture of a footy the sharp bow is well dug into the water and acts as an airfoil (hydrofoil) with a sharp leading edge. Rapid, deep stalls and changes of direction. We certainly get this but my explanation may be childish.
The downwind waterlines of my razor and Sloice are behind the mast - see
Added note - the “darting” is not Sloice, but the driver! I was using the TX upside down left-handed while holding the camera with my right paw:D
One combi-cure is to move everything aft, thus getting the bow well out of the water and sailing (for most of the course) a footy with as short waterline, large rocker and very close-coupled foils. Doesn’t seem to harm the downwind either!
andrew
Hi Peter and Clare,
One thing I would comment on is the size of your hatch. More hatch area, while convenient for access, offers more places for water to leak in. Lightweight Footies are particularly sensitive to added liquid displacement. For a hatch I use a 4" plastic can lid with a combing of G-10 or 1/64th aviation plywood that matches the lip of the original can. It is a light (all of 7 grams for lid and combing together), removable, and watertight.
Progress update.
Slow but painted.
Hull painted minus hatch 57g compared to 54g at the same stage with HOP2IT version 1.
Better paint job (more weight) but less epoxy sealing the inside.
The hatch weighs 8g but doesn’t include the two 3mm nylon screws.
Version 1 only had a piece of plastic and tape so the overall increase in weight is 11g, not bad for a larger hull.
Niel unfortunately it is too late to look at a different hatch arrangement this time. On one of the other threads a footy hull was given a very short half life so it won’t be long until version 3.
Regards
Peter & Clare
Hey Peter & Clare - Thats a looker alright! She gives the appearance of speed even up on the blocks. When you get her sailing please post some photos of her, as well as both versions sailing together, and a comparison report. I am sure that readers here are as curious as I am to see if there is any evident improvement in V2.
First sail of HOP2IT2 today.
Light conditions, wind strength between zero and nothing.
Eventually we did get a couple of weak gusts.
All up weight 416g, 14g heavier than version 1.
4 X AAA NiMH batteries instead of LiPo.
Hitec HS85 servo repaired with metal gears on main sheets.
Different sail, longer foot, lower centre of effort, approx same area and the same camber and twist.
Trimmed stern low at rest, see pic.
No water leaks with the hatch but we would have had to throw a bucket of water over it because no water even got onto the deck.
Much easier to sail than version one, less weather helm and tacks easier.
When there was a gust it did move along but needs a better day and version one to compare with.
Shows potential.
Next time one of us has to sail and photograph at the same time. Should be interesting.
Regards
Peter & Clare
Finally sailed the two boats together.
No doubt that HOP2IT2 is faster in all directions however this isn’t very significant as we have rigorously applied exacting scientific method to the development.
This method is where you change as many parameters affecting as many variables as possible at the same time. Then you draw as many improbable conclusions from the results as you can.
Lets see.
HOP2IT2 is
longer, less beamy, more freeboard, more rocker, the fin is further aft, sail shape is different!!!
It has the same equipment, weight, sail camber and twist.
Apart from that you can easily see that they are almost the same.
We also made an internet course and had to find a different lake to use it.
Best times from the first attempt
Clare 4:22 HOP2IT1
Peter 4:25 HOP2IT2
Consistency is a major issue at the moment.
Both for us and the weather. It is common here to have becalmed and knockdowns in the same run.
We have had some issues with windward performance. Through a number of changes without attention to detail we ended up with too much sail area ahead of the pivot point. After re-reading some of Brett’s posts we are starting again on rigs and sails.
Regards
Peter & Clare
P & C - It does take a while to shake things out, but a couple of pretty and pretty impressive looking boats for a pair of new builders and sailors. Congrats!