folding prop Martec Elliptical versus Flexofold

[Jim Cate]

i believe that at very low speeds the biggest influence on boat drag is skin friction, not prop drag. At high speeds, as you approach hull speed, then wave making consumes the most power. it is at the intermediate speeds where the folder adds the most to one's performance.

The dramatic improvement in my racing standings came racing in SF bay, not a light air paradise! Where I believe the biggest incremental gain was in windward legs at less than hull speed. Both speed and pointing ability improved in my case.

Jim

[robert sailor]

Originally Posted by Jim Cate

i believe that at very low speeds the biggest influence on boat drag is skin friction, not prop drag. At high speeds, as you approach hull speed, then wave making consumes the most power. it is at the intermediate speeds where the folder adds the most to one's performance.

The dramatic improvement in my racing standings came racing in SF bay, not a light air paradise! Where I believe the biggest incremental gain was in windward legs at less than hull speed. Both speed and pointing ability improved in my case.

Jim

I have no problem accepting that but tell me what time of the day were you racing and was it in the summer or winter?. I found that after lunch that bloody wind kicks in and I think I could have gotten hull speed dragging a pail, LOL. I never experienced the props helping pointing that much but you have lots of experience and I have no reason to doubt you. My personal experience has been racing in light airs in the Vancouver area and the boats with fixed props are really left behind in a big way however when it really blows the odd time we find that some of the boys with fixed props are right in there. I'm a bit out of date but you used to get 3 seconds for the difference between a fixed and a folder but in actual sailing its not even close.

[Jim Cate]

Originally Posted by robert sailor

I have no problem accepting that but tell me what time of the day were you racing and was it in the summer or winter?. I found that after lunch that bloody wind kicks in and I think I could have gotten hull speed dragging a pail, LOL. I never experienced the props helping pointing that much but you have lots of experience and I have no reason to doubt you. My personal experience has been racing in light airs in the Vancouver area and the boats with fixed props are really left behind in a big way however when it really blows the odd time we find that some of the boys with fixed props are right in there. I'm a bit out of date but you used to get 3 seconds for the difference between a fixed and a folder but in actual sailing its not even close.

Well, the short answer is that the ocean races tended to start around 1000 IIRC and some of the bay races started later. Some of them went all night, some were shorter. We raced year round. And yes, in the winter the winds are often lighter, unless a winter storm is around, and then they can be even stronger than the summer sea breeze that we enjoyed so much.

The boat involved was a yankee 30, and I raced in the Single Hand OYRA ocean series, the Yankee 30 one design bay races and lots of special event races. Busy, busy... long ago when I was young and energetic!

As to where the prop helps most, I think referring to a yacht design book would likely clarify that issue. I don't have such on board, but my memory of the issue is as I said: at low speeds skin friction dominates, at high speeds wave making dominates and in between parasitic drag from props, keel and rudder vortex generation and so on adds up to dominate the sums.

I thinkk Marchaj reflects on this in one or more of his books, read decades ago! Doubtless other folks have done so as well.

Jim

[robert sailor]

Originally Posted by Jim Cate

Well, the short answer is that the ocean races tended to start around 1000 IIRC and some of the bay races started later. Some of them went all night, some were shorter. We raced year round. And yes, in the winter the winds are often lighter, unless a winter storm is around, and then they can be even stronger than the summer sea breeze that we enjoyed so much.

The boat involved was a yankee 30, and I raced in the Single Hand OYRA ocean series, the Yankee 30 one design bay races and lots of special event races. Busy, busy... long ago when I was young and energetic!

As to where the prop helps most, I think referring to a yacht design book would likely clarify that issue. I don't have such on board, but my memory of the issue is as I said: at low speeds skin friction dominates, at high speeds wave making dominates and in between parasitic drag from props, keel and rudder vortex generation and so on adds up to dominate the sums.

I thinkk Marchaj reflects on this in one or more of his books, read decades ago! Doubtless other folks have done so as well.

Jim

flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf

This is about the most comprehensive tests done on props. Makes a good read for the fellow who started this thread and certainly proves why we both like the Flexofold props. Not interested in getting into a debate but it does state in the copy that the folders have their greatest percentage savings at low speeds. That aside you sure were dedicated to be racing single hand, something I have never done. The Yankee's were great boats and well built as I remember, we sailed in loose company with a Y36 on one of our trips to Hawaii and it did very well.

[sailsw00]

I recenlty researched new folding props for my Catana, and decided on the Flexofolds. Less that three days after they got my credit card info, the UPS man delivered them to my house, all the way from Denmark. I'm impressed.
-Steve

[keeljoy]

I've though the fixed prop would also be a buzz kill in currents. We have a lot of tidal action at Shilshole as well -- as the sound is narrow where we race.. We're sailing Non flying sails this session. Once we get that down we'll probably purchase an asym spinnaker

[robert sailor]

Originally Posted by keeljoy

I've though the fixed prop would also be a buzz kill in currents. We have a lot of tidal action at Shilshole as well -- as the sound is narrow where we race.. We're sailing Non flying sails this session. Once we get that down we'll probably purchase an asym spinnaker

Just don't bother racing with a cruising chute as the handicap allowance is not adequate compared to a racing chute. The currents and the local knowledge play a big role in racing outcomes. Enjoy yourself, once you get it dialed in that Ranger should sail easily to its handicap.

[Kiwi.]

Originally Posted by keeljoy

All well thought out comments. I noted on Monday that I finished 5 minutes actual and 3 minutes corrected 5th of 5 boats 14 minutes behind the leader. If I had gained .5 knot from a folder I would have won the whole NFS class by 2+ minutes and corrected to 5+ minute win.

You're obviously keen on your racing, as I was for many years, even as an amateur. Get a Flexofold 2 bladed racing prop. They are worth the extra money.
We used to put a swimmer over before a light wind start to put rubber bands over the non-geared two bladed folder on our Farr 38. For a Fiji race (from Auckland NZ) one year ,we took it off altogether.
If you think about it all fixed props are specifically designed for maximum grip on the water, and that means maximum drag. Until you approach hull speed there can be easily half a knot between a folded two blade and a fixed three blade; I'd rather tow a bucket of the same diameter as the prop behind my yacht than have a fixed three blade under me.

[George DuBose]

Pearson 36 with a 2 blade Flex-o-fold. I love it.

...but if you want your boat to point higher, tighten the rigging...

[u4ea32]

Originally Posted by Jim Cate

As to where the prop helps most, I think referring to a yacht design book would likely clarify that issue. I don't have such on board, but my memory of the issue is as I said: at low speeds skin friction dominates, at high speeds wave making dominates and in between parasitic drag from props, keel and rudder vortex generation and so on adds up to dominate the sums.

I thinkk Marchaj reflects on this in one or more of his books, read decades ago! Doubtless other folks have done so as well.

Jim

Well stated, Jim.

The reason a folding prop helps pointing is because pointing is all about lift-to-drag.

If you have too much drag, you cant point at all, like an old fat square rigger, or when flying a full symmetric spinnaker. The best pointing boats - the foiling AC wing masted boats, or foiling kite boards with high performance kites - minimize both hydro and aero drag.