Return to Hobie.com

Hobie Forums

It is currently Fri Apr 20, 2018 11:08 am

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 337 posts ]  Go to page Previous  1 ... 12, 13, 14, 15, 16, 17, 18 ... 23  Next
Author Message
 Post subject: Re: TI outboard mount
PostPosted: Fri May 26, 2017 9:08 am 
Offline
Site Rank - Old Salt

Joined: Thu Jun 01, 2006 1:16 pm
Posts: 520
Location: Colorado
I didnt study what you want to do with the gas cap long enough but one thing that would be important to me is that the gas did not leak when the outboard was shut off and rotated up (prop not in the water) for sailing mode..

What I do now is to open the vent on the cap when the outboard is running but I close the vent when I rotate the outboard up. I also close the vent when I store the outboard and that along with using Seafoam keeps the gas left in the tank fresher.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri May 26, 2017 9:14 am 
Offline
Site Rank - Captain

Joined: Mon Nov 02, 2015 9:59 am
Posts: 87
walt wrote:
My opinion.. - since I have the Suzuki and use the stock prop and only one outboard.

Remember that to go some speed, you need some horse power. Horse power is RPM times torque. In order to get max HP with a piston engine, you need max explosions per second and that is around 6000 RPM for either the Honda or the Suzuki. And, to get the max HP, the torque must be the maximum the outboard can produce at that peak HP. If you either can not get to 6000 RPM because the the prop pitch has too high of torque or the prop does not produce max torque and the outboard rev limits (the Suzuki will do this, the Honda does not), you also can not get max and rated 2.5 HP.

Back in this thread a ways, I tested the Suzuki stock prop - one outboard and on a TI. The 2.5 HP outboard with the stock prop at wide open throttle got the prop RPM just a little under 6000 RPM. This is just what you want to get maximum HP and maximum speed out of the TI. Peak speed with just one person sitting in the back seat - 7.5 to just under 8 mph.

On the Suzuki, the stock prop is just about what you want. If you were to change this prop to a higher pitch, this is what would happen.

1. The higher pitch prop would produce higher torque at a given RPM so now you would no longer be able to get the wide open throttle RPM up to near 6000 RPM. If you can not get up near 6000 RPM, you can also NOT get up the rated HP out of the outboard. On the Suzuki, this means that if you increase the pitch of the prop over what it is now, you are NOT going to get the same peak speed because you will produce less HP.

2. If you operate the outboard at less than peak HP and peak speed such as 6 mph which is lower than the peak 2.5 hp will achieve, you also do not need to get to peak RPM. So at 6 mph (significantly under peak speed), the higher pitch prop would result in lower RPM and the outboard would likely be less noisy.

3. For either pitch prop, you need to produce some HP to go some speed. The outboard may or may not get slightly better fuel efficiently at lower RPM but the bottom line is that it still needs to produce the same HP to go that speed. So the higher pitch prop might give slightly better fuel efficiency but it just would not be much.

4. For a given HP out of the outboard, since the higher pitch prop result in lower RPM, it must operate at higher torque (remember HP = RPM * torque). So all the components of the outboard have higher torque and higher strain. At some point this is not good for the outboard. However, its likely you really have to increase the pitch a lot before you would have a problem.

My opinioin.. the prop on the Suzukin 2.5 is about perfect for the TI application


Walt, good explanation.
I have Suzuki 2.5 with the AI2, here is what I observed.
1/4 - it goes to 5.5knt about 6mph
1/2 - it goes to 6knt
3/4 - it goes to 6-6.2knt. Too much vibration, and not much speed gain. I see the prop spin like mad, but it does not push the boat any faster.
Full - it goes to 6-6.5knt. I feel that the engine is about to explode any second.

I feel that if I change the prop to a bigger size, it will have more thrust to push the boat faster during higher RPM. Can you confirm this?


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri May 26, 2017 9:27 am 
Offline
Site Rank - Old Salt

Joined: Thu Jun 01, 2006 1:16 pm
Posts: 520
Location: Colorado
Since you have the Suzuki 2.5 hp, it has a rev limiter built in (uses the electronic ignition) so will not rev over 6000 PPM.

I should find the video I did earlier (its in this thread) but I first put the outboard in neutral and ran it up to rev limit which is 6000 PPM. I know this is 6000 RPM because I had checked this earlier with a Oscilloscope.

I then ran the TI at wide open throttle getting to almost 7 knots - not much different than you got - and the RPM sounded to be just under 6000 RPM. Just going by sound is not super accurate.. but I think it was over 5000 RPM

If you go to a higher pitch prop, at a given RPM, the torque will be higher. You might assume that higher torque at 6000 RPM gives more HP but that is not true. The outboard will NOT produce more than 2.5 HP (unless you start modifying how fuel is delivered).

If you increase the pitch of the prop, you will now get lower RPM and will no longer be able to get the rated 2.5 HP. So my opinion is that if you go to a higher pitch prop, you will have a slower peak speed.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri May 26, 2017 9:34 am 
Offline
Site Rank - Captain

Joined: Mon Nov 02, 2015 9:59 am
Posts: 87
walt wrote:
Since you have the Suzuki 2.5 hp, it has a rev limiter built in (uses the electronic ignition) so will not rev over 6000 PPM.

I should find the video I did earlier (its in this thread) but I first put the outboard in neutral and ran it up to rev limit which is 6000 PPM. I know this is 6000 RPM because I had checked this earlier with a Oscilloscope.

I then ran the TI at wide open throttle getting to almost 7 knots - not much different than you got - and the RPM sounded to be just under 6000 RPM. Just going by sound is not super accurate.. but I think it was over 5000 RPM

If you go to a higher pitch prop, at a given RPM, the torque will be higher. You might assume that higher torque at 6000 RPM gives more HP but that is not true. The outboard will NOT produce more than 2.5 HP (unless you start modifying how fuel is delivered).

If you increase the pitch of the prop, you will now get lower RPM and will no longer be able to get the rated 2.5 HP. So my opinion is that if you go to a higher pitch prop, you will have a slower peak speed.


Then I'll just save my money not buying another prop. Cheers.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri May 26, 2017 6:34 pm 
Offline
Site Rank - Old Salt

Joined: Thu Jun 01, 2006 1:16 pm
Posts: 520
Location: Colorado
I could of course be wrong..

But if you do get a higher pitch prop, first do an accurate speed measurement with your current prop in no wind and no current (like you have done).

Then put on the new prop and repeat holding every thing else constant so the only change is the prop.

I think the current prop on the Suzuki 2.5 is about right in size and pitch if your goal is to go as fast as possible. Im not even sure they make other pitch props for that outboard (which might be a hint that the stock one is just fine) so you may pay $$$ for something custom.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Sun May 28, 2017 2:40 pm 
Offline
Site Rank - Captain

Joined: Wed Jun 01, 2016 7:11 pm
Posts: 57
Location: North Jersey/NYC
So here is my idea and I am putting it to the test as I write this. Back in the days, I bought 3 small Honda generators and installed them on my trucks (semi trucks) for the purpose of creating an auxiliary power unit. These generators had an aftermarket cap with a fuel line built into it. When connected to an auxiliary fuel tank (which I fitted all 3 with), it would siphon fuel into the generator just because the declining fuel level in the generators would create vacuum which would pull fuel even if that external tank would be positioned lower than the generator (which was the case in all 3 generators).

I though I could apply this principal here as well. When researching it, I read those Honda generators had a built in fuel pump and that what actually pulled the fuel into the tank (and not the ventury effect the carburetor provide). The Suzuki fuel is probably gravity fed but I decided to try it anyway. BTW, my diesel mechanic killed my idea and told me the motor would starve. I thought if that would be the case, I can fit a manual or electric fuel pump and replenish the 1 litter the Suzuki hold every so often. I am using clear tubing so I can see the fuel level.

The principal is very simple;

* I am running a line from the auxiliary tank to the cap through a quick sprayless connector I found on Amazon (when disconnected, both ends are sealed).
https://www.amazon.com/gp/product/B007G ... UTF8&psc=1
This tube goes through the cap and reach deep into the bottom of the Suzuki tank.
* Another tube is coming out of the cap. on the inside of the cap, it is flush with the surface. on the outside, it is connected to a shut off valve on one side, and via an adapter, to a larger diameter clear tube.

BTW, it is running for 30 minutes now with the auxiliary tank positioned lower than the motor. My hopes are getting high...

Operation:
* Before starting, and upon connecting all the lines, open shut off valve and suck out of the wider tube. This will pull fuel from secondary tank and fill up the Suzuki tank. When fuel will come out the cap. Push air back into the tube, drop the fuel level below shut off valve and immediately close valve. This insure the Suzuki tank is completely full and fuel system is primed.
* When done and want to put motor away, open shut off valve, blow air through the hose, and push all the fuel back into the secondary tank. This would leave very little fuel in the outboard which means no need to condition the remaining fuel if stored for long time.

BTW, the motor is working for over an hour and a half now. I am shutting down. The fuel line is fully primed. Did I mentioned the secondary tank is a foot lower than the motor this whole time? I think it is safe to call it a success :idea: :idea: :idea:

Image

Image

Image

Image


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Sun May 28, 2017 4:13 pm 
Offline
Site Rank - Old Salt

Joined: Sat Nov 05, 2011 1:58 am
Posts: 2734
Location: Forster, NSW, Australia
I think I will just stick to emptying one of my 1 litre aluminium fuel bottles into the outboard tank every hour or so. I have an outboard mount on my TI's trailer, so I store the outboard upright on there when the TI is on the trailer. Simple.

_________________
Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker and Hangkai outboard
only cool people follow the (non-magnetic) titanium weight-loss program! lol.)


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Sun May 28, 2017 5:02 pm 
Offline
Site Rank - Old Salt

Joined: Sun Apr 20, 2008 6:18 am
Posts: 2803
Location: Sarasota,Key West FL
Tony:
Yea that's what I do too, I can tilt the outboards up when sailing and transporting but long term (like in the garage) I always tilt them down for storage.
Since I started running ethanol free recreational gas (available at some gas stations here) I no longer drain the carbs during storage.
Though I've been thinking about adding fuel filters that would separate any water in the fuel.
FE


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Mon May 29, 2017 2:54 am 
Offline
Site Rank - Old Salt

Joined: Thu Aug 16, 2007 2:25 pm
Posts: 2676
Location: Central Coast NSW Australia
Hezi wrote:
So here is my idea and I am putting it to the test as I write this...
...BTW, the motor is working for over an hour and a half now. I am shutting down. The fuel line is fully primed. Did I mentioned the secondary tank is a foot lower than the motor this whole time? I think it is safe to call it a success.

Congrats on this impressive and innovative mod, Hezi! 8) Clever design with the dual role of filling and draining the tank.
Personally I haven't found filling the tank every 75 minutes too much of a problem but well done with what you have come up with!


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Mon May 29, 2017 6:39 pm 
Offline
Site Rank - Captain

Joined: Wed Jun 01, 2016 7:11 pm
Posts: 57
Location: North Jersey/NYC
Thanks Stringy. I agree the 1 litter container is the simpler way to go. So far I've been using a 2 Gallon fuel tank I got at Home Depot. Refueling is such a pain, and in cold and high sea, I just gave up. Yes, if I prepared 1 Litter bottles in advance it would have been a breeze. For my application and for going on a full day on the water, when I need to use the motor often, an "unlimited" range can be very convenient. Besides, I have everything ready short of the marine tank (on order from eBay) and replacing that week clear fuel inlet tubing into something more rugged.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Wed May 31, 2017 1:39 pm 
Offline
Site Rank - Old Salt

Joined: Thu Jun 01, 2006 1:16 pm
Posts: 520
Location: Colorado
Im trying to understand this..

First, if that fuel system is gravity feed only, I think it could pull some fuel from the auxiliary tank but dont think this is sustainable. Ie, I dont think just gravity alone of the fuel going into the carb could pull say three of the outboard tank fulls out of the aux tank. Remember you said the aux tank is lower than the outboard tank. I believe Siphon action would only work if the aux tank level was higher than that the outboard tank level.

If you are pulling fuel from the aux tank, work is being done and this requires a power input. So I guess this means that there must be some sort of fuel pump in the Susuki outboard that creates the vacuum and hence the power to move the gas? Is that fuel pump just the carb sucking gas as it runs?

Another question on the 1.5 hour test. We know that under about half throttle or so where the outboard is generating power and doing work to make the TI go maybe 5.5 to 6 knots, it will run for in the range of 80 minutes. Lets take a wild guess here and estimate that the outboard is generating 1.5 HP to do this.

So in the test tank, is the outboard still generating 1.5 hp? Or is the HP actually much less since you are just circulating water? If the outboard is generating much less power, its not hard to imagine the small tank on the outboard lasting 1.5 hours.. Did you happen to check the gas level in the tank after it ran for 1.5 hours?

I really like your experiment, good for you for trying it out. The things I have questioned Im not sure about so please keep that in mind.. I may have it all wrong..


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri Jun 02, 2017 5:38 am 
Offline
Site Rank - Captain

Joined: Wed Jun 01, 2016 7:11 pm
Posts: 57
Location: North Jersey/NYC
Hi Walt, every thing you wrote is valid. I also thought running it for 1.5 hours in a little over idle speed shouldn't exhaust the fuel. But with my setup, I emptied the motor tank from air with only one clear hose as an inlet (remember, outlet was shut tight by a valve). Throughout this whole time, the inlet hose was primed with fuel. There was no way for the motor to work such long time regardless of RPM without pulling fuel. This little toy motor wouldn't run against vacuum in the fuel system otherwise. When I stopped the motor, I couldn't just open the cap since the tank was full and fuel would spill. I had to open the valve and push air which pushed most of the fuel back to the secondary tank.

I talked to Rocco my diesel mechanic and told him it worked against his theory. He said the motor must have a fuel pump to keep working in the conditions I put it under. My motor is 2016. I have a service manual for older motors. There is a round part on the carburetor I couldn't see on the service manual. I texted Rocco a picture. He claim it's a vacuum fuel pump. Maybe he is right. Here is a picture, do you have it on your Suzuki? I know this outboard didn't change much over the years, and I wander what year is your motor and if this round part exist on on it.

Image


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri Jun 02, 2017 11:10 am 
Offline
Site Rank - Captain

Joined: Mon Nov 02, 2015 9:59 am
Posts: 87
My 2015(may be 2016) suzuki 2.5 also has that fuel pump.

Curious, has anybody adjust their fuel mixing screw?
Mine idle rough, and shut off in gear when not opening throttle. It's fixed when I open the screw 1/2 turn.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri Jun 02, 2017 1:15 pm 
Offline
Site Rank - Captain

Joined: Wed Jun 01, 2016 7:11 pm
Posts: 57
Location: North Jersey/NYC
Can you post a picture of it? My motor gave me hell last time. I had to alternate chock on off and play with gas to warm it up before putting in gear (which will kill the motor again) over and over to the point of exhaustion. The next day my upper body was so stiff, it wasn't funny. I knew it's an adjustment issue and I did turn the screw for the idle to raise RPM but didn't see mixture screw.


Top
 Profile  
 
 Post subject: Re: TI outboard mount
PostPosted: Fri Jun 02, 2017 2:46 pm 
Offline
Site Rank - Captain

Joined: Mon Nov 02, 2015 9:59 am
Posts: 87
The problem is due to emission control. The engine runs lean from the factory. Need to give it more gas for it to be happy.
Drill the aluminum cover, go very very slow.
Turn it 1/2 turn-counter-clockwise. Run it about 10 minutes to warm up, then adjust the idle speed.



Image


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 337 posts ]  Go to page Previous  1 ... 12, 13, 14, 15, 16, 17, 18 ... 23  Next

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
© Hobie Cat Company. All rights reserved.
Powered by phpBB® Forum Software © phpBB Group