R-27/OB Throttle setting causes RPM/Speed to slowly increase

[baz]

Subject: R-27/OB Throttle setting causes RPM/Speed to slowly increase

So I'm getting more and more use on our new R-27/OB.... and was out today with 4 adults and 3 children onboard. Weather was glorious with full sunshine, with little wind and fairly calm sees with the odd swirly currents and 1 or 2 foot chop at times. No swells to be of any concern. Had around 120 gallons of fuel, 35 gallons of fresh water and maybe 4 gallons in the holding tank. My guess would be the boat weighed some 9500 lbs without people and children on board.

So this was a good opportunity to see how this wonderful R-27/OB performed with its awesome F300 out back and more importantly how it behaved under these very favorable weather/water conditions on the Puget Sound around Edmonds, Kingston, Port Madison, Agate Pass and Poulsbo and back to Edmonds. We made the round trip after having dropped our crab pot for an overnight sinking/soaking. Will go back tomorrow to see what keepers turns up. :lol:

First, this R-27/OB is simply a joy to drive. It's rock solid with a bit of leaning now and then as people moved around in the boat. It becomes more stable as speed picks up. Manual steering is at times stiff (but not overly so) and then slackens off. I cannot explain why this happens.

At 30+ mph my son and grandson wanted to know how fast we were going. It seems at around 30 mph there's a strong sense we are moving fast.... it could be the look of stern wake and the rush of air through the boat... but dunno.... I just comment on the fact that when picking up speed to 30 mph and above people such as my son and grandson became aware of the increased speed. I held the F300 trim (the up/down on the throttle lever) set to a constant 3 bars throughout the trip.

Now to deal with the Subject line.... Whenever I set the throttle lever to a specific position and left it there I notice the engine RPM and resulting speed would slowly increase....and this is with me not touching the throttle lever at all. Thus, lets say when I set the throttle lever when my speed was at 25 mph and left it there within a few minutes the RPM will climb and the speed will obviously increase. This was a bit concerning for me as when the speed and RPM increased to cause the boat to go faster than I wanted I had to back off the throttle to reinstate the starting speed I thought I had set to begin with. I'm wondering what causes this affect.

BTW.... at 30 mph today the boat was displaying around 2 mpg and this was from around 1.4 mpg at 20 mph. It seems the boat does better as the speed goes from 20 to 30 mph. At 30 mph the boat levels out a bit and becomes more rock solid than at 20 mph where it had a tendency to bounce a bit. The 30 mph speed was more comforting for me because of this.

At the helm I found that standing was better for me than sitting as standing I felt more in control of things as well as having a better view over the bow. When standing I could lean back some and rest my bum on the lip of the helm seat.

I have to say, getting around my local Puget Sound in a timely manner is really a big benefit for me.

This boat makes very gracious and secure turns when at speed.

Now and then we would hit a stretch having 2 to 3 feet waves and slowing down to a 15 to 17 mph was needed. At these speeds the boat handled very well and rocked and rolled no more than in my R-25 running in similar water conditions.

It was a good day on the water with this new R-27/OB. RT has really done a nice job with it.

After tomorrow we will be looking forward to going up the Anacortes - Cap Sante for Tuesday night and then will be motoring up to Roche early Wednesday to the Rondy to meet up with some 200 boats and around 400 people, so I'm told. Woweee.

 

[ixlr8]

Subject: R-27/OB Throttle setting causes RPM/Speed to slowly increase

Now to deal with the Subject line.... Whenever I set the throttle lever to a specific position and left it there I notice the engine RPM and resulting speed would slowly increase....and this is with me not touching the throttle lever at all. Thus, lets say when I set the throttle lever when my speed was at 25 mph and left it there within a few minutes the RPM will climb and the speed will obviously increase. This was a bit concerning for me as when the speed and RPM increased to cause the boat to go faster than I wanted I had to back off the throttle to reinstate the starting speed I thought I had set to begin with. I'm wondering what causes this affect.

Barry, I noticed the same thing on my test runs, on both the 23 and the 27OB. The feeling I had was that it took a minute or two to settle in to being on plane at that speed. I know that doesn't make much sense, but that was the feeling I had. After it settled in, if I brought the throttle back to get the speed I wanted, then it seemed to stay there.

 

[Brian B]

The type of prop could have something to do with what you describe. My buddy has a Yamaha and was running a 3 blade prop. With the 3 blade the motor would not hold RPM, he was always adjusting the throttle. He changed over to a 4 blade S.S. prop and when the throttle is set it stays there in all types of sea conditions. He told me he lost top end speed by 2mph but the increased torque was well worth the trade off.

 

[Red Raven]

Maybe it has something to do with engine temperature. As the engine warms up when set to a higher throttle it may get a bit more efficient. If you don't touch the throttle does it eventually stabilize as the engine temperature stabilizes?

Interestingly our classic R27 does this at WOT. It will start out at 3850 rpm and then slowly climb to 3950 (or even to 4050 when really clean an less load). It does not do it however at lower throttle settings.

 

[baz]

At the Rondy next week Yamaha will be there to discuss engine maintenance and what not..... I will be asking Yamaha about the slow increase in RPM with a fixed throttle position to see what they have to say and what is the explanation for this. Me wonders which tail is being wagged. Is it the boat encouraging more RPM or is it the engine doing this on its own ?

 

[baz]

BTW.... I've not played much with the UP/DOWN engine trim and have had it left set at 3 bars for all of my boating so far.

Just what are the Pros/Cons for using this engine trim feature. I know it alters the thrust vector about the boat's CG so I'm thinking it simple will adjust the bow up/down attitude. Maybe it will also adjust fuel burn as well as it could also affect the amount of hull surface to water ratio.

 

[baz]

Oh.... one other thing to note.... It's very important to know where the neutral position is for the engine lever. On my R-25 and R-21EC the neutral position was with the throttle lever in its vertical position. With this Yamaha the neutral position is with the lever about 10º off vertical in the aft direction. This is important for docking when angling the F300 to move the stern one way or the other with the use of forward and reverse settings. Just a slight nudge for forward from the neutral and just a slight nudge aft for reverse. It takes practice to get comfortable doing this. I'm getting better with every docking activity as I stern into my slip with a starboard tie.

 

[tpfahy]

Same phenomenom on the R23. Changing the trim via tabs or engine tilt does the same. A gradual increase in rpm and speed. Ease back on the throttle and enjoy the extra MPG. A static throttle with some trim tweaking on a 70 mile leg on auto pilot can see speed increase and rpms increase or decrease by several mph or several hundred rpm. MPG can increase by 15-20 percent. Find your sweet spot. There is a small cover on the side if the electronic throttle where you can adjust resistance with a small Allen wrench. I remember a lock and tension screw. Easing tension made docking and backing into slips much easier.