TI outboard mount

Walt, it is all rather simple.... the theoretical hull speed is that which sees length of the bow wave exactly matching the waterline length of the hull. As speed increases, the bow wave lengthens, and no longer supports the stern. Therefore, the vessel then begins to run >uphill< as the only the bow is supported. The longer the bow wave, basically the steeper the "climb".

This why they talk of a boat "climbing up on the plane"

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

yep.. https://en.wikipedia.org/wiki/Hull_speed

What is interesting about that is that something like a displacement hull sailboat will not exceed theoretical hull speed by much at all. I have a 26 foot sailboat with a 9.8 hp outboard on it which is about twice the HP that boat needs and it gets up to about 3% over THS with the outboard at full throttle.

If you go 22% over THS (which is a significant amount), you cant exactly call that a displacement hull especially considering that a very small outboard was used to achieve this.

Pictures from this afternoon - no motor and no mount, just sail and pedals.

That is the beauty of adding a small outboard to our Islands... none of the inherent charm and enjoyment of the design is compromised, while the availability of power adds considerably to the versatility. My motor spends most of its time tilted and silent.

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Agreed Tony!

Yep.. adds some versatility. There was some discussion on how the outboard gets used on these boats. On smaller lakes I leave it at home (nice the "micro" outboards dont weigh much). Or if the sailing club has a get together, also leave the outboard at home. Its big (or long) water where its nice. One trip is up the Colorado river below Lake Mead and you motor first to get about 10 to 12 miles up river (against current), then shut the outboard off, lift it out of the water and have about the nicest possible sail back.

The other way I used it so also on a long lake where we just followed the wind for a bunch of hours not worrying about how far we got or if the wind died. Near the end of the day, drop outboard in and motor back at 6 knots.

These pictures are of the trip on the Colorado river where I also towed an AI. Hope to do that trip again this fall. First picture is motoring up river towing the AI, second picture is sailing back down with the motor tilted up and out of the water.

I think the problem we have in sw fl and the keys is the great distances we need to trave to get anywhere of interest. Very few launches that are near anything of interest (unless you like shallow bare white sand (nothingness)),and thru most of the year our winds are 3-7mph most of the time we want to go out, (probably 8-10 months a year).
The other difficulty is it is very hot here and really sunny nearly all the time. This means you are peddling along at 2-3mph in 90 plus sun and heat 8-10 months out of the year. I've suffered heat exposure several times tryin to get my 10-15 peddling miles a week in (my exercise program).
Another thing that I think might be percular to our area is the terrible washing machine chop whenever the wind gets over 10mph, making the TI very uncomfortable to operate with my bad back.
We don't fish at all, but we are very big into snorkeling and scuba diving (our favorite pastime). Unfortunately it's extremely boring snorkeling and diving in totally bare sand in 3ft of water. As an example We have been in Florida bay several times, and I don't recall ever seeing an actual fish, I'm sure there are plenty, we just haven't seen any, compared to other places we go.
Many days we are going 50-60 miles round trip to get to the places we like to hang out and meet up with our powerboat friends.
We were recently at lake Hartwell in Georgia on holiday which is over 40 miles long. We wanted to explore and go see the dam one day, we went over 20 miles that day, and never even got close to the dam dam, cool place though.
Since our TI is now our only boat now, it is relenquished to the task as our general purpose family boat, called upon to do whatever we happen to be doing that weekend. The boat is so versatile it's rediculous. We never know what configuration we will need especially when camping. We have had our TI out one day scuba diving the coral reefs near akey West, then the next day quietly peddling the sante fe river in kayak mode, then the next week we ran the rapids of the Huron river, then a few days later made the run out to Macinac Island, all on the same boat.
We have a blast with our TI, and having the motors on it, makes the boat that much more versatile when we need them. Same applies with our massive sailsets, especially in our typical light winds, you can actually get places in light winds, of course if the winds pick up you just put the big sails away (most of our sails are on furlers and you just spin them in and out as needed). Using the best sails for the particular conditions we are in.
I really hate the noise outboards make at high rpm, so we have our motors re-propped so 80% of the time we only run them just above idle (extremely quiet, probably equal to a Torqeedo in noise output). At low rpm we get around 2-3 hrs of run time per tank of fuel (each tank is 1qt). Very seldom do we have to refuel on the water, I usually carry on board 2.5 gallons of gas (just in case), I think that will get me 150-200 miles range in a pinch if I need it.
Of course you can just tilt the outboards up and not use them at any time.
FE

I lifted the mount 50mm by adding another section of post tube underneath. After another 10 hours of motoring covering nearly 80km I am happy with this setup. The extra height makes it is much less prone to getting hit by waves, especially when heeled over.


The turnbuckles needed lengthening so I added shackles. This worked but also added weight so I went to a more conventional bracket type setup using u-section aluminium.




The bracket weighs 2.6kg and can be removed easily by undoing 2 eyebolts, a quick release pin on a turnbuckle and a wingbolt.


I have been really enjoying this outboard on the TI. As has been said, the touring range has been greatly increased. We are now able to access spots that previously used to take days to get to. Motor sailing in light winds is easy.
It has a shallower draught than the pedals and works well in water too shallow for the rudder. It is also a great benefit when the wind is really strong. I've taken to motoring into a strong wind and then sailing back.
Here is a mix of clips: motoring, sailing and motor sailing.
This outboard just adds so much to an already versatile craft. The only downside really is the noise but this negative is outweighed by all the positives IMHO!

Very impressive, Stringy. For the first time, a little outboard has my attention. Nice job.

Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

I'm sold too Keith, even though I went the cheap route. My sub $200 Chinese two stroke outboard is loud but its 3.5hp has plenty of grunt. Only weighing 9.7kg is a bonus.

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Me too, always good to have as a back up....

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2015 Tandem Island - Golden Papaya "HALIBOO"
(retired) Outback - Hibiscus Red

An interesting thread. After reading this my previous idea that electric power was the way to go has been challenged.

One observation that I will make is that I always thought that the 9.8 outboard on my previous trailer sailer was much too big till I found myself motoring out of a narrow channel into a strengthening afternoon breeze. I needed all the power the engine had and made very slow progress. It was an exciting sail home when I got back into the lake and could get the sails up! My point being that while you might only need 1/4 throttle for normal cruising the power reserve is still necessary as the mast and hulls can creates a lot of drag.

Another observation is that what is being reported as cavitation (which is where the water boils on the low pressure side of the propeller) is most likely to be ventilation where air is sucked down from the surface. This is made worse by putting the motor at the end of the boat where hull movement increases the partial "surfacing" of the propeller. This was quite a problem of my last boat. Mounting the the motor closer to the centre of the boat would alleviate this but probably introduce other compromises?

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Brad K
Papaya Tandem Island - "Dry Reach"
Lengthened Jet Ski trailer
"Kayaking Bob" Spray Skirts
Trampolines

I don't seem to be witnessing any consequences with my motor mounted midships. Sure I don't think it is very effective for steering, but I get the super convenience of (literally) using it as an elbow rest, can spin it round for reverse, can start and stop it, and refuel it. When I tilt it, I turn it sideways to minimise interference with the water. On starboard tack the leg never touches the water, but on port there is a bit of drag.I probably could mount the motor a little higher, but that would require some re-engineering.

Of course some conditions can exceed the capability of little motors... my local lake roars in or out through a narrow channel at up to nine knots. My 3.5hp motor can only do 5.2 knots at present (only 2 tank fulls to date) so I need to consult the tide charts to ensure realistic passage making.

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Im not aware of anyone having a cavitation issue with these really small outboards. I have been using mine mounted just behind the rear seat and it never cavitates. You can have some cavitation when applying very high hp to a prop.. but we are only talking about 2 to 3.5 hp here. The pressure stress on the props is orders of magnitude under what would be required to cavitate.

Also on my sailboat (with a 9.8 hp outboard), I can get the prop to cavitate by doing a tight turn in wavy conditions where the prop gets near the water surface. You can easily both hear and feel this happening because when air gets sucked down to the prop, the torque immediately is reduced by a huge amount and so the outboard rpm increases rapidly.. I have NEVER had this happen with the 2.5 hp outboard on the TI.

On TI's with the motor mounted on the side, you kind of need to have the motors a little deeper in the water in order to compensate for the boat leaning on one tack or the other. What I do is mount my motors as close to the hull as possible, I also tilt the motors slightly so the props are under the hull.
In my case I modified my motor mounts so when the motor is mounted it is angled about 5 degrees, with the props slightly under the boat.
I typically lock the motors straight and steer with the boat rudder with no issues. Even on a tack with the boat tilted I'm not hearing any cavitation (you can usually hear prop cavitation clearly).
In the event of rudder failure I can always steer with the motors if needed (a reduncy feature). If one motor fails I can operate off the other and still get back to safety (triple reduncy).
The cool part is if I have enough wind I can simply tilt the motors up and sail the old fashion way, Having the motors on the boat tilted up don't effect the performance of the boats sailing ability at all, actually having a little extra weight at the stern seems to help performance (I'm a front seater).
FE

Thanks for sharing the photos of your new mount, Stringy.

I've gone the PVC route and didn't even think of aluminum as a candidate. The ingenuity of folks on this forum is a continual source of new ideas (and enjoyment) to me.