An RG65 from the main hull of a Volans Trimaran
I started this story on the multihull section of the forum, but thought that it made more sense to start a new thread in the RG65 section. The story so far: I purchased a Volans trimaran with the intention of seeing if it could be modified to go a bit faster, and to see if the floats could be used to make a catamaran. This story is on-going and I’ve started a new thread entitled Epsilon Volantis A in the multihull section of the forum. Pondering what to do with the main hull it occurred to me that it might be possible to convert it into an RG65. With no experience with monohulls the first iteration was a disaster as I tried to put a wing sail on it, but the rig was to heavy and the boat wasn’t capable of staying upright.
I have now spent more time working on fitting out the hull and building a conventional rig, trying to recycle as many parts as possible from the Volans:
The hull and deck require some more sanding and repainting/varnishing, but the boat is now almost ready for testing, requiring only sail. I intend to post some videos in the hope that someone who knows something about monohulls can provide some advice to help optimise the performance.
Some basic data to begin with:
Length: 650 mm
Beam: 90 mm
Weight: 1015 g
Bulb weight: 500 g
I’m happy to provide any other information on request.
One feature worth noting - a Huon Pine (the best boat building wood on earth) laminated deck.
With the sails finished I’ve taken the boat out for its maiden voyage. The final weight with sails was 1048 g.
Some footage below:
Forgive the poor sailing, it was the first time I have sailed a rc monohull. I would be interested in any suggestions as to how the boat (or my sailing) could be improved. Keep in mind that I’m not necessarily trying to make a competitive RG65, but rather I’m trying to get the best performance I can out of this hull. A couple of things that were clear to me: excessive weather helm; rudder movement not sufficient for adequate control.
For those interested and with some stamina, I’ve up loaded a longer unedited clip:
Some changes to reduce heeling:
- Sail area reduced from 1840 cm2 to 1570 cm2, by removing material from the top of the sail (jib now 31% of total sail area);
- Volans keel replaced with more conventional keel 28 cm long. Total area (including bulb) 98 cm2.
- Volans rudder replaced. New rudder 11 cm long. Area - 33cm2.
- Combined area of keel and rudder = 8% of total sail area.
- Mast moved forward 1.5 cm.
- New weight = 980 g.
She looks tender in the vid even with lots of twist in the main … maybe problem could be righting moment is too light @ the bulb end.
If you divide the total weight of the boat by the combined keel/bulb weight this ratio should ideally in high % (60-70+%) otherwise reducing sail area (as you have been doing) is another one other option.
Yes the bulb is a bit light, only ca. 51% of the total weight. Unfortunately I’m a bit limited due the the narrow hull. The longer keel and smaller sail seem to have improved things quite a bit. The footage below is pretty poor, conditions weren’t ideal so I only had the boat in the water for a couple of minutes, however, it was clear that the heeling had reduced. Unfortunately it was also clear that there was now excessive lee helm. I think that I had better do some calculations to fix this, and stop guessing.
I agree with Alan that you have excessive heeling. This means you are not able to point close to the wind with the sails close hauled… You do however have great acceleration in the moments when it all comes together.
As I see it, there are a couple of basics to get less heeling and thus more control:
1: Reduce the sail area and/or lower the centre of effort - longer but lower sails would help. More easily said than done. If the mast is self supporting (or by adding shrouds aft of the mast) so you do not need a backstay, you could have a longer mainsail boom with less height - even a gaff shape… This increase in sail area aft of the mast and the resultant shift in centre of effort down and back could be compensated forward of the mast by expanding the jib foot moving jib centre of effort forward, maybe even using a bowsprit and/or multiple overlapping jibs
2: Increase the righting moment by adding to the underwater structure. I would assume it is not practical to increase the bulb weight as that will pull the hull lower in the water. This means you would need to extend the keel fin. To be extreme, consider doubling the length of the fin - this is the same effect as making the bulb twice the weight… this of course leads to issues of excessive draught so you will run aground sooner…
A combination of these is probably the answer.
Congratulations on your innovative ideas, following with interest…
Thanks for the suggestions, I hadn’t thought of increasing the lower area of the sail.
Being from Tasmania, I’m surprised that you didn’t back up my provocative statement regarding Huon Pine:D.
Good wind for testing and CLR and CE better aligned:
I need to sail it against some other RG65s to make a real assessment. The weight seems a bit high for the volume, and it tacks a bit like a multihull, but it seems to be quite quick downwind. Overall, I am confident it will serve it’s purpose as a learning boat for monohull sailing.
During the build I came across a post from Dick from 2007 discussing RG65 designs: "Given the current (unlimited) rules, my initial thought for a personal boat was a very thin/narrow hull, easily powered and similar to an “A"Class catamaran hull relative to their narrow, wave piercing hulls, and with similar length/beam ratio. With such a narrow hull, the deep (currently unlimited ) depth keel would be required for stability, but limited bulb weight for displacement reasons would become a critical design decision/trade-off.” I think that it sounds pretty much like what I’ve got.
This boat is now finished with the hull tidied up and painted. Final weigh 1030 g. I’ve taken some footage of the boat sailing (below). As I noted before, it seems quick down wind, but tacks poorly, nothing particularly suprising given the lack of rocker. It seems to nose dive quite a bit, but with the wave piercing bow, this doesn’t seem to slow it down too much. I’m interested to see how it performs against other RG65s. My guess is that it will be ok down wind, but struggle to keep up into the wind. If I do get to compare it with other boats I’ll update this thread with a summary of the preformance.