TI outboard mount

I'm starting the process that will result in casting plastic props for the Honda 2.3 mounted on our TI. I've used Smooth On products with good success in the past - quite an interesting company - so I'll design and build a prototype, make a mold, and then cast the props. My knowledge of outboards and props is limited at this point, so research is my first stop:

1. It sounds like a 7 inch pitch is the target. (yes/no?)
2. Does the number of blades (2 vs 3 vs 4) matter?
3. Does the "depth" of the prop matter?
4. Does the thickness of each blade matter?

I'm interested in any and all help. Thanks!!

Yeah, they are remarkable. FE's been kind enough to take me out with him twice. His wing foresail is a remarkable bit of kit. I think we saw 5 mph (measured via GPS on eTrex) on that foresail alone and not a lot of wind. That wing works well in a motorsailing application, especially when combined with the added flotation and flattened stern profile that he has.

You really need to measure RPM of the outboard first with the stock prop before doing anything. If the current prop is hitting 5000 to 6000 RPM (check the outboard specs to be sure), then you already have a well matched prop for the vessel you are putting it on.

At wide open throttle and you are measuring RPM

If the RPM seems to peak out too soon and hitting near 6000 RPM and before WOT and staying there, you likely are rev limiting and the pitch of the prop needs to be increased.

If the RPM at WOT is UNDER the rated RPM (usually 5000 to 6000), then you have too high of pitch and need to go lower.

Assuming that Honda had no clue about the right prop for that outboard is likely a poor assumption. I think the prop that comes with the Suzuki 2.5 is just about right for the TI. Since I have not measured RPM.. I could be off. And.. the only opinion I would completely trust is someone who did an accurate job of measuring BOTH RPM and speed.

FYI, you can get a very cheap RPM meter that has an internal battery and a sense wire that wraps around the spark plug wire. However, this instrument has different settings as a two stroke will fire the spark plug every rotation and a four stroke might only fire every other rotation. If you get the setting wrong, you get readings way off (like 1/2).

I will add that on a lot of displacement sailboats, people will run a prop that is too HIGH of pitch. The outboard cant get up to its full rated RPM but maybe still close. Example, you might only get up to 4800 RPM rather than 5500 RPM. The reason for this is that the sailboat generally does not need the full RPM to go "hull speed" and the higher pitch prop results in lower RPM for a given speed. The benefit is lower noise and lower vibration. A lot of stock small outboards come with prop pitches that are actually a little too high to hit peak RPM on a sailboat hull - but the outboard doesnt make as much racket for motoring.

FYI, here is the tachometer I mentioned earlier (Kedsum) http://www.amazon.com/KEDSUM-Tachometer ... B00ACDP6YU The 2.3 Honda is four stroke so I think you would need setting three which is i pulse every two revolutions.

Here is another way to look at the need for the RPM reading. That outboard puts out a maximum of 2.3 hp - no more. It puts out that maximum hp when some load (a prop) puts the maximum amount of torque load that still allows the outboard to reach its peak rated RPM. The max HP for a given boat speed comes from the prop that allows the RPM to get up to just under 6000 PRM (the Honda also specs 5000 to 6000 RPM).

If you put that outboard on a boat that only gets up to 5 mph with 2.3 hp, it will need some pitch prop to achieve the full RPM and 2.3 hp.

Now if the outboard is used on a different hull that will go 10 mph with 2.3 hp, the water is moving by the prop a lot faster so a higher pitch prop is needed to get up to the peak RPM and 2.3 HP.

If you take that outboard out with a particular prop that gets the RPM full throttle to just under 6000 RPM, that outboard is doing that speed with its maximum 2.3 hp. You can NOT get more HP out of that motor without modifying it. That is the fastest you will do without going to a higher HP outboard. Changing the pitch to either higher or lower will only result in less HP and slower speed.

Anyhow.. if the reason for designing a new prop is to go faster, my opinion is start by measuring the prop Honda engineers thought was best. You likely are right that the pitch could go up a little from what comes stock but if the stock prop is getting anywhere near 5000 RPM and also not over revving trying to go past 6000, I dont think you will get much at all extra speed by messing with the prop.

Good way to learn about props.. hopefully you do try your experiment.. I found my Kedsum tach.. why Im not sure.. but I probably will put it on my Suzuki 2..5 with the TI just to find out where things are at with the stock prop that comes with that outboard.

Thanks, Walt. No, my reason for the new prop isn't to go faster per se, it's to keep the motor from cavitation and over revving when I'm motor sailing.

Walt:
Interesting discussion, I can see you have put some thought into the discussion. Everything you are stating is exactly correct if you are using the outboard as your primary power source. In my case I'm not I only need the engines to provide 40% of my power requirements, which works out to around 3/4hp from each engine (1.5 total hp). This is enough to propel the boat to my threshhold speed of 6mph, at just above idle (around 1000 to 1200 pm on the motors). That threshhold speed is the minimum speed that my wing needs to operate (think of the wing similar to the wing on a piper cub airplane, on a plane your prop creates forward propulsion (not the wings). You have to be moving about 50 mph for the wing to operate, if you are flying and the engine quits you fall out of the sky, in my case if I stop peddling or the engines quit the boat just stalls and stops dead in the water. The wing just operates as a simple energy amplifier not too different from a heat pump (a heat pump takes existing heat in the air and amplifies it. The purpose of the wing is to take existing wind plus the wind created by your forward motion and combine organise and amplify this wind into something useful (apparent wind). In my rudimentry phase one design I simply drive this accelerated and aligned air over the back side of the mainsail (as if the air was coming out of a hair dryer) now moving nicely at around 9-10 mph in 2-3 mph natural winds, basically tricking the mainsail to think the winds are 9 mph. I'm sure you have tried to sail in 2-3 mph winds, the sail just luffs like a flag and does nothing. I can easily sail at 2-3x windspeed, actually my best point of sail is almost directly into the wind because I can generate the most apparent wind into the wind.
P
My boat is configured as a tri-powered human, sail, plus some supplimental power from either my hybrid gas motors or battery electric motors. Actually I can eliminate the motors alltogether with two strong peddlers, however we get all pooped out in about a mile or so (thus the need for the supplimental propulsion, simply because I am no athelete and never will be) however I am able to peddle at a sustained pace of around 40-50 cpm (cycles per minute) for up to around ten hours with a few short breaks once in a while so everything was designed around my own physical abilities.
The normal cruise speed on my boat is 8-10 mph, I determined that to be my minimum cruise speed in the hot florida sun ten months out of the year regardless of actual wind speed and direction.
When I got my first TI in 2010 in order to buy the boat I committed to pedal the boat 15 miles per week as my exercise program. With the stock TI the first two outings I got blown out to sea and couldn't get back to shore. What I didn't realize at the time is the typical winds around here 10 months out of the year are only about 5mph. In 5mph winds the boat pedals at around 3mph and it takes all day in the hot 92 deg sun to get your 15 miles in. I suffered heat exhaustion several times that first summer. Now I still try to go out every weekend (weather permitting) but now I get my 10-15 mile in a couple hrs. Some days I do 50-60 milers.
I don't use my engines for anything else. I always measure my distance, speeds, and precisely measure my fuel used each outing and get a pretty consistant 100mpg which equates to about 3-4 hrs runtime from each 1 quart fuel tank, most weekends I burn about a quart of fuel (about $.50 to $.75 cents in fuel), I can afford that.
Hope this explains something, I have no clue what it all means to anyone else and don't really care, I just setup my boat to solve my individual problem and it works great for me, everyone else can do as they please with their boats.
FE

Bobagain:
Thats pretty much why I had to re-prop my engines, I've exploded several engines powersailing. Just a hint on a stock Honda with the standard 4.5 inch prop goes boom and explodes at a little over 10 mph powersailing.
My current setup with the the 33sq ft wing and 90sq ft main the boat tops out at around 15 mph so you have to have minimum 7 inch pitch props or the engines go boom.
When I add my big spinnaker the problem gets worse, with all 260 sq ft of sail in really good winds the boat tops out around 20 mph, so when I have the spinnaker installed I have to put the ten inch pitch props on the boat.
All these props need to be custom made to match the motor hp (pitch vs prop diameter vs number of blades, blade sizes/surface area,etc).

FE

I used to ice boat and land sail and boats with wing masts would of course do many times the speed of the wind. A common configuration was a single high aspect sail using a big wing mast (very specific accurate shape) with a soft sail behind the wing mast. The big wing mast sail has both good lift but also a good lift to drag ratio. These sails dont create something out of nothing, they simply create lift and drag like any other sail. All the equations for lift and drag have a wind velocity square term. So components like drag must be kept as low as possible because of the wind square term - all those forces go way up as you start going fast. So the sails must have a very high L/D. The wind moving over the sail creates a lift vector and if this has a component in the direction you want the boat to go, it will. As you go faster and faster, the apparent wind clocks around to being more and more on your nose simply because of your own boat speed. Since the sail must operate with some angle of attack with respect to the wind, the sail angle also clocks around with the sail force vector also clocking around. As the boat speed gets higher and higher with respect to the actual wind speed, the sail force vector in the forward direction gets smaller and smaller until finally a balance is met between the boats/sail drag and the forward component of lift. If all drag components are kept small, this can be many times the wind speed These sails dont do anything that would seem to violate the laws of physics like "amplify the wind", they are just able to extract energy out of the wind at higher speeds and have as low as possible drag components (drag also goes up with wind velocity square).

Windsurfers for years tried double surface sails and you can also find a bunch of patents filed for double surface sails but about the only thing that stuck in the market were "camber inducers" that forced a two surface pocket behind the mast. People tried those more wing shaped sails in speed trials and they didnt produce - and went away. I personally took camber induced windsurfing sail to about 5X wind speed on ice and land and single surface windsurfing sails will also get close to this. Its all about low drag to do this (which we dont have on the water unless you go to foils).

So anyhow, I am very skeptical about the wonderful things you claim your wing jib does, Adding sail area definitely helps go faster in light winds and you get a benefit from a foresail/ mainsail arrangement. But all my experience says that the two surface wing shaped sail might have incrementally better L/D but it just might mean you would slowly pass someone who was using a single surface jib - and only very slowly pass them. Using analogies to explain anything is a bad idea as an analogy can be just plain wrong but sound good. The claims just doesn't match what Ive seen with land sailing and windsurfing over the years. You do of course get an incremental benefit from a wing sail over a single surface sail but you need to be racing to tell this. Hopefully speeds posted are actually measured and not theoretical. Theoretical speeds can be seriously off reality but sure sound good.

And.. I dont like to get into arguments and so Ill just post my opinion on this without saying yours is at all wrong. Its just a forum where someone can read stuff and different opinions are a good thing.

FYI, Bobagain, my opinion (and I put that in there because I dont have a link to back this up) is that these props with only a couple HP driving them just dont cavitate. You get cavitation when you seriously stress pressure boundaries by using a prop to deliver LOT of HP. We are a huge way off from needing to worry about cavitation with only a couple hp. Regarding the over rev, I dont think I have this problem with the Suzuki 2.5 on the TI also motor sailing and maybe you do with the Honda but you really should try and measure RPM to know for sure. Having that measurement will add a lot of confidence to your results if you make the higher pitch prop.

Thanks, gents.

I'm planning to get that "tach", Walt, (although, I may build one once back in PA) which should provide precise data. Nothing more fun than a little field testing. I guess a wind measurement system would help as well.....

Since I recommended the Kedsum.. I tried to get mine to work this morning with the Susuki 2.5. Ive tried wraping the sense wire around the spark plug wire several different ways (all with three to four wraps) and the Kedsum doesnt seem to be able to pick up the signal. I was using this same instrument back in December on a Nissan 9.8 HP and it was working so Im not sure why I cant get it to work now.

The one I bought also has an internal non replaceable battery - which I thought was OK since I got the info I needed from the 9.8 HP. Seems odd that it would be bad now just sitting inactive for a couple months and the display still works when I press the buttons. It did get beat up a little, maybe I damaged it.

Anyhow.. some risk in buying that instrument.. and your backup method would be good to have even if the Kedsum works. The Kedsum has some settings like 1P1R or 1P2R (or something like that) and I interpreted that to be 1 pulse, 1 revolution or 1 pulse 2 revolutions. Some four stroke fire the spark only every two revolutions since the power cycle only occurs every two revolutions. But some four strokes also fire the spark every revolution because.. its simpler to implement. The extra firing doesnt do anything, just something to consider for measuring RPM.

Anyhow, if you measure the RPM, I will find that very interesting!! I probably will keep trying a little with my Suzuki 2.5 to do the same.

Walt:
I'm sure you are correct in everything you are saying. Prior to making my wing sail about 3yrs ago now, the previous 3 yrs I was running just a single surface jib around the same size. Actually I have never sailed my TI without a jib mounted since the first two outings where I got blown out to sea and couldn't get back in, then a few more times that same spring (2010) where I suffered heat exposure a few times.
Just because of the geography of the area I find myself sailing up wind 90% of the time mostly in very low winds (that just the area we live in).
When I built my wing jib I based the airfoil shape on the eppler 420 airfoil shape. The jib only operates in a narrow band, mostly upwind in the typical under 7mph winds we have around here. It seems to do a better job than my old jib but that could all be my imagination.
Maybe I'm not really sailing 15-20 degrees off the wind at 8-10 mph in 5mph winds, I apparently just think I am, and the sails are just along for the ride (doing nothing).
It does seem strange though I have the same routine every weekend (I try to peddle my boat 10-15 miles per week average year round weather permitting).
Every weekend I do exactly the same routine. I launch the boat with all the sails furled. I then adjust and lock the throttles so the boat is going exactly 6 mph (measured on gps, the harbor is pretty protected from wind and waves). There the throttles stay for the rest of the day (just above idle, which gives me typically 3-4 hrs of run time per tank). The engines with their underwater exhaust appear to me anyway to run very quiet. All the time I am out I pedal at a fairly steady 40 to 50 cps (walking pace), thats my exercise. I then go out in open water and sail to the best of my ability all the wile peddling at the same pace with the engine throttles locked.
I constantly watch my gps and the boat appears to average between 8-10 mph pretty much all the time I'm out. With a little wind it goes a little faster, with less wind a little slower (but not much). Even on the days with only 3mph winds and very flat water my average speeds remain pretty close. Typically if the wind is over 7 mph I stay home.
I monitor my speed on my gps constantly, and it automatically records my distance traveled and my average and max speed for the day. I sail around until I get to either 10 or 15 miles (depending on my available time) then I go home. I've posted probably 30 videos on the forum all doing the exact same thing, all extremely boring to watch). I always measure my fuel usage, nearly every time I use a half of each 1 quart tank, sometime a little more sometimes a little less. The fuel economy seems to be pretty consistent. Some weekends I'll do 50-60 milers sailing up to Egmont key and back (but that can get boring). The worst point of sail on my boat is a broad reach, the boat goes much slower and I appear to consume much more fuel.
I prefer low winds and flat water because of my bad back. The boat can take much more than me, but that's just my preference.
When we go to our Key West house we configure the boat differently, I usually bring my big 135 sq ft spinnaker along (great trade winds off of key west), and we usually go off shore to the reefs all loaded down with people and gear to go scuba diving and snorkeling (our favorite pastime).
That's what we do with our boat, I can't explain it, but it works well for us. As boring as all this sounds we have a blast with our TI and love it. I don't really care what anyone else does with their boats, ours works for us. I only share on the forum because I was asked to by other members a long time ago. I just share what I do, and like to read what others are doing with their boats, and try to help with suggestions where I can.
I only posted about the prop pitches because I've exploded several engines now, and the pitches I ended up with were derived via very hard and expensive knocks).
You sound very experienced and knowledgable, and can figure all this stuff out yourself, as you figure stuff out just post about it, we are all interested, and yes we do listen.
FE
Here is a video of me just bopping about (one of 30 or so videos all posted here showing all the same boring crap). You might notice their are 200 sailboats out, and I'm doing triple the speed of any of them.
https://www.youtube.com/watch?v=AaaBSQtlcA8


Here is another one almost the same crap different area different day. After posting the video I discovered my modified hull had came loose on the bottom of the boat, and was catching water like a sea anchor, killing my fuel economy, I was perplexed why I was only getting 30 mpg that day, after repairs things went back to the normal 80-100 mpg.
https://www.youtube.com/watch?v=iX-i4ffbllY


Now here is a really old video from 2012 (before getting my wing sail, and sailing in the same waters as the second video, in pretty close to the same wind conditions (just look at the water around the boat to get a read of the wind).
https://www.youtube.com/watch?v=zW62S1_RfYQ


Now finally a video of my spinnaker (which I don't use often anymore). This is the same general area as video 2 and 3 with similar winds around 5 mph. Notice I'm not getting anywhere very fast, yea I'm sailing 1=1 to the wind, but even at that, it makes for a very long day.
https://www.youtube.com/watch?v=XRQdfhZXCVk


Now here is an interesting video from when I was doing sea trials on my wing jib design 3 yrs ago. If you watch the AMA in the video you will note their is almost no heeling side force (making the AMA go under water). I thought this was interesting because my single surface jib with full sail and jib (same size) out would have been burying my AMA underwater. Why all this occurred I have no idea.
https://www.youtube.com/watch?v=ETwxZZMtyxg


Now this next video was during prototype testing of the wing, the air induction system was not installed yet, and the wingform shape was not the eppler 420 airfoil form (something much less (naca 2105 ( I think)). I later figured out in winds over 10-12 mph the 33 sq ft jib alone has pretty much the same power as the 90 sq ft main all by itself, even though it's only 1/3 the size (basically I can sail at the same speeds). I have no clue why, it just works. Actually if it gets really rough and windy I always put the main away completely anymore and only fly the jib, I've had it out and fully tested it in 35 mph winds and 4 ft seas.
Again I really don't know why, it just seems to work.
https://www.youtube.com/watch?v=ETwxZZMtyxg


This is the only video I have of the wing jib furled up on the furler system (I seldom bother with using the furler, I just wrap it around the mast and drop it on the hull)
https://www.youtube.com/watch?v=buWkPhcRuOQ




What all this means I have no idea, I'm just havin fun (somethin to do).
FE

FE, I worked my way through those videos and always enjoy that. Interesting and innovative!

I tried to get that Kedsum tach working again this morning. The sensor is a sheathed wire set that you are supposed to wrap around the spark plug wire 3 or 4 times and I tried a bunch of different ways of doing this and I can finally get it to wake up (it starts on its own when it detects a signal) but I just cant get it to give reliable readings. Sometimes they jump all over the place, sometimes when steady its clearly a wrong reading..

So.. I give up on that instrument. The outboard is in the back yard running in a bucket (the Suziki has a water pump so MUST be run with the pump in water or it ruins the pump very fast). This outboard is a little different than the Honda in that it has a gear shift (neutral and forward, NO reverse - you rotate the outboard 180 degrees for that). So I put the outboard in neutral and revved it up until I can hear the rpm limiter kick in. Before the rev limiter kicks in, it runs smooth but in rev limit, you can hear it running slightly different - like some timing is off or something. As I mentioned before, I had an oscilloscope on my Nissan 9.8 watching the signal to the coil and it looked like the way the rev limiter worked is to measure RPM and then screw up the spark timing to limit the RPM. The little Suziki does "sound" like it does the same thing but that is also a guess since I didnt do the same Oscope measure.

On my 9.8 Hp Nissan, I did the same thing with very similar sounding results except that I was measuring RPM on the Nissan and the rev limiter kicked in right at about 6000 RPM. For whatever reason, this is a very typical number for at least these small four strokes and I think my Suzuki also rev limits at 6000 RPM - but I can only go by sound.

So.. tomorrow we are taking the TI out with a couple other TI's and also a few sailboats and doing a long down wind run to a cove where the sailboats are camping for the night. We are going to motor back. So.. I will do an experiment and take some video/audio of the outboard in neutral and revved up until it limits. I will then run the outboard at full throttle on the TI (there will be two of us on the boat) possibly with and without the sail up (depends on conditions), take more video/audio

Im not sure if this will tell me anything but Im hoping to be able to watch (listen) to the video in rev lmiit and then running the boat and possibly determine if Im in rev limiting. If I am in rev limiting, I would likely benefit from a slightly higher pitch prop. Or.. just keep doing what I do now and run the outboard at about 3/4 throttle where its definitely NOT rev limiting and seems just about right.

Fun day yesterday sailing the TI with my wife. No motor and no mount. We sailed in some strong winds, the TI is a great boat for those higher winds..

So to be a little more accurate with my own measurments.. I checked the Suzuki 2.5 hp to see where the rev limiter was set.

I put an oscilloscope on the drive to the spark plug coil and with the outboard in nuetral (no load on the prop) right at where I can hear the outboard limit RPM, the pulses were at 99.2 Hz.

If we convert 99.2 pulses per second to pulses per minute (multiply by 60), this is 5952 pulse per minute. It looks like the spark is fired every revolution and that the rev limit is set at close to 6000 RPM. This matches the outboard specification.

Interesting also was to watch the spark timing when the outboard went into rev limiting. Right at 6000 RPM, the pulses are very close to 10 msec apart. When the outboard went into rev limiting and you could hear it not sound so good, I measured the timing between a few of the pulse. Remember just before the rev limit, the pulses were very evenly spaced 10 msec apart. When I tried to go to higher throttle setting, first pulse was 10.8 mec, second was 8.08 msec, third was 9.36 msec. So I think its a good assumption that the electronic ignition module is measuring RPM (it has the right input signal) and does something to the spark timing to keep the outboard from over revving.

So... I am pretty sure I will be able to hear when the outboard reaches 6000 RPM and starts to limit just be hearing.

an oscilloscope..you have an oscilloscope...NOW I'm jealous!!

That scope has a 3.5 inch floppy drive.. its a little old.

Here is where we are heading to tomorow (link from a facebook picture, you may not be able to see it??)

This picture is about 3 weeks old..