how to adapt a higher pitch prop to bf 2.3 Honda

[fusioneng]

I need help, I have a Honda BF 2.3 motor on my Hobie Tandom Island sailboat, currently I have a Honda bf 2.3 motor on the boat. The boat currently top out at around 20mph, and I have blown one engine already over revving (the stock prop on the BF 2.3 is 7 1/2 dia 4.5 pitch). I currently have a Tohatsu 7 1/2 x 7 pitch retrofitted on the motor (easily adapted). However I desperately need at least a 10 inch pitch propeller ( Like I said I have already blow one motor exceeding the RPM). My plan is to mount twin bf2.3 motors with 10-12 inch pitch propellers. The boat is a hydrofoil boat with wing sails so the motors are not my primary propulsion so I don't need high horsepower engines, with my current setup I run the engine at 1/4 throttle (the boat weighs 200 lbs and is 18.5 ft long) and with the wing sails I travel 8-10 mph in low winds (under 8mph) and get around 100 miles per gallon fuel consumption. My plan is to add the second Honda 2.3 motor so I can cruise at 20 mph and get around 50 miles per gallon. When not planning to go far offshore I can always leave one motor at home, or just don't drop it in the water when not needed (we sail mostly off shore South Florida Gulf coast and Key West).
Of course the boat is only plastic, and I can't stand any more weight than what the twin Honda 2.3 motors would be back there. I already have the twin engine motor mount made and one Honda, as soon I get the propeller problem solved I will add the second Honda 2.3.
I talked to Honda and they do not provide any propellers besides the stock prop for the BF 2.3. So my plan is to make an adapter to put a 3 blade 9" x 10" pitch prop (probable from a Honda 8 to 10 hp) then turn down the OD to below 8 inches.
The question I have is, Has anyone tried making adaptors (or can you buy) so you can use a different prop from the original.
That's all phase II, in phase III I plan to put on at least 12 pitch propellers onto the twin engines, install my existing hydrofoils onto the boat so the boat rises out of the water (eliminating the hull displacement problem, and drag from the hull), and try to cruise at 30 mph (at 50 plus miles per gallon).
Any suggestions on where to go to get the propeller adapters.....
Bob

 

[Sea Rider]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Welcome to Iboats.

How can you possibly cruise at 20/30 MPH with 2.3 HP motosr being around just 70 CC ? Not even with 4 of them..Will need to take engine along to measure prop sahft diam & splines, take new prop to measure hub diam and splines and make a proper adapter at a machine shop. Strange that Honda only fabricates one single prop for that model, should have some more to play with rpm and pitch accordingly.

When you have resolved all about the new propellers, you'll need to install an induction tach for each engine, go for a wot spin you alone and lightly loaded sib and check max achieved rpm to see if inside min-max wot safe parameters, best all around performer would be near or around max rpm wot rpm numbers factory stated for that engine. If you been using combo without a tach on first motor, engine probably didn't went caput by over revving, probably by extreme lugging which can also ruin an engine, too much stress on pistons and crank shaft. But that will never be known..

Happy Boating

 

[steelespike]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

It appears he runs with the sails and the motor apparently a planing hull.
If the sails help too much he apparently easily over revs.
The boat also has hydro foils that can lift the boat clear of the water.

 

[Sea Rider]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Fusioneng,

Is the plan using both 2.3 motors to push better the sailboat when with no wind or sailing without sails ?

Some tech issues that don't match at all :

-Useless running engine(s) on on a sailboat that's doing 20 MPH on a water course. Won't add more MPH
-Will produce unwanted tail darg and slow the sailboat a bit.
-Will need minimum a L or a XL motor to compensate engine height once hydrofoils have lifted the sailboat.
(2) X 2.3 HP engines although will sum 4.6 HP will not achieve double speed, will have better torque to push sailboat much better, but slight more top end speed than with just one.

Happy Boating

 

[fusioneng]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Sea Rider:
30 mph plus would be with twin engines not one, and would require me to have my hydrofoils mounted under the boat to lift the entire boat out of the water about a foot to eliminate the drag from the hull, that's all phase III in the future (not now). I've been running the boat this way now for about 4 yrs (with the single engine, but I only added the wing about a yr ago). The front sail is an actual wing (about the same size as the wing on an ultra light airplane (actually very similar to an ultra light wing), except it's mounted vertically). On an airplane you have to use your engine to drive you forward fast enough for the wing to lift the aircraft, if the forward motion stops the plane drops like a rock. I have exactly the same situation. Without the motors running and just pedaling (two people) we can get the boat up to around 6mph, which is the bare minimum for the wing to start working. Unfortunately at that pace pedaling I can't sustain that speed that long without getting exhausted, so what we do is run the motor at 1/4 throttle, this propels the boat if no sails are up at all to around 3-4mph, (of course if I open the throttle wide open with no sails at all the boat speeds up to 8-9 mph, but I burn through the 1/3 gallon fuel tank in about 20 minutes, I prefer that 1/3 gallon to last me 3 hrs (that's what I get with current setup)). When I start pedaling at a sustainable pace, the boat speed up to around 5 mph (minimum take off speed for the wing to start working). The wing works on what they call apparent wind (the wind created by your forward motion). Now if you have 5 mph of natural wind coming at you, the actual wind going over the wing is 2x windspeed (your forward motion 5mph plus the 5mph natural wind, this is why airplanes always take off upwind). The boat averages 7-10 mph in no to low winds, of course if there is a lot more wind everything is amplified much more, the wing is safe to operate, and has been tested in up to 30 mph winds. In this area 11 months out of the year that's all we have is wind 3-6mph, plus with more wind comes way more big waves, so we don't typically go out in high winds at all. In 20 mph winds the boat easily does 20 mph with or without the motor with 265 sq ft of sail area, but I don't like to go out in those conditions offshore, basically I'm all rigged for the no to low winds we typically have ten months of the year.
How everything works, I'm not asking about (I've been using most of what I have with no issues for a long time), I was just wondering how to adapt a big prop not designed for this motor onto this small tiny motor if anyone had any tricks or experience with off the shelf adapters or something.
Perhaps if I show a video of a typical day on the water it will help https://www.youtube.com/watch?v=bDGNxvCyVeI.
Bob

 

[Sea Rider]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Bob,

Congrats on that nice vid and sailboat set up. What type of propulsion does the pedals move under the hull ? Have you installed a remote control box for gearing and throttling the engine that far away fom cockpit ? On vid you mentioned too much motor drag, will need to raise motor accordingly untill a near flat water bed is achieved at back motor.

Happy Boating

 

[fusioneng]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Sea Rider:
Thanks it's just a hobby and exercise program for me, I'm out there every single weekend pedaling the stupid boat 15-30 miles all year round. In Florida there is very little wind (typically around 6mph ten months out of the year), the stock boat with none of my modifications will go .6 times windspeed (actually I can peddle faster than I can sail in low wind). I'm a destination type of person (we like to go off shore scuba diving, and Island hop around the keys. Out in the hot sun with no breeze it's like being an egg in a frying pan out there, plus I want to get where I want to go in a reasonable amount of time so we can dive. If it takes 3 hrs to get the 10-15 miles out to the coral reefs from the launch, then another 3 hrs to get back it's hardly worth the trip. With what I have with good trade winds I can get out their in under an hour, a little longer on a no wind day. Basically my only cost is the dollar in fuel for the day as compared to the $800 bucks it would cost us to take a commercial dive charter, or rent a powerboat for the day (about $800). We used to have a 24ft Sea Ray (60k) plus $350/month for dry storage, plus a couple grand /yr for maint if your lucky (which is ridiculous in salt water), Then we would burn up 60 gallons of fuel over the weekend (@ $4.50/gal at marinas), it just got so out of control we simply couldn't afford it any longer. So we the this TI which is like a family SUV, we use it for pretty much everything we used our powerboat for, plus half a dozen other things. We have actually been out scubadiving with 4 people 10 miles off shore, then the very next day my wife and I kayaked up the Sante Fe river (there are a bunch of crystal clear springs on the river), and were in Colorado the following week running rapids (with out the sails and AMA's of course) (true story).
The Hobie Mirage drives are like penguin fins that swing back and forth under the boat, very efficient, both me and my wife can pedal for ten hrs one day then get up and do it all over again the next day when are doing expeditions up rivers and stuff. The boat comes stock with two sets of penguin fins, which is the primary propulsion of the boat (it's a pedal boat, not really a sail boat). I just happen to have mine all mod'ed out and hardened for offshore use (stock the have a CE "D" rating). All my junk was added 4 yrs ago because I got bored very quickly putzing along at 3-4 mph, and wanted to use it offshore.
It sounds like I just need to order a couple props, then just make my own adapter to make them fit my motor (just like I did with the Tohatsu props). I was just hoping somebody had an off the shelf solution that I could just bolt on (I'm not all that familiar with all the prop options out there), and am a little frustrated at Honda for not providing any alternate prop options, not every needs to push a 1500 lbs bass boat at 3-4mph, my boat only weighs 200 lbs.

 

[fusioneng]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Sea Rider:
Good suggestions, you are correct I am just dragging that motor thru the water at higher speeds (huge amount of drag from the lower unit, you can see it in the video) once the chain reaction has occurred and the perpetual motion from the wing has me going at cruising speed, the motor is just dragging in the water anyway. That's how I over revved and blew up my first engine). The faster I go the higher the engine revs, even though it is locked on 1/4 throttle (until boom ( LOL))
I do have a remote throttle up in the cockpit where I can control the throttle and kill the engine. I typically just lock the rpm at 1/4 throttle currently, and just leave it alone for the rest of the day. I will add a couple Bimba cylinders and some hydraulic line up to the cockpit with a rotary hydraulic positive displacement pump (like a power washer pump) so I can tilt the engines up and down from the cockpit. I suppose I can run a remote starter rope up to the cockpit as well, so I can start the motors as needed as I'm pretty sure I can't tilt them up while running. Currently I start the engine when I get on board then just let it run all day (at idle when not going anywhere of course).

 

[funk6294]

Re: how to adapt a higher pitch prop to bf 2.3 Honda

Have you tried taking this to someone at a prop shop and explain what your looking for? While I realize there are no off the shelf solutions for this application, I wonder if they could repitch your current 7 pitch prop a little higher, or even offer some other suggestions.

Additionally, I am not sure that you will ever stop the over rev situation with the sails pulling the boat faster than the engine. Think of it like a car going down a steep mountain, if the roads steep enough it will cause the speed to increase past what the motor can provide as a brake.