Prop or is it something else?

I don't understand why SR uses a ratio for a smaller engine than MerC usually matches up with. Our 1.62 is a V6 ratio behind a V8 and your 1.81 is a 4-cyl ratio behind a V6. But both are Brunswick companies and I suppose they work out what they want.

I did read where MerC specified a lower gear ratio (higher number) for "high altitude" operation...

Our SR is bottom painted with "hard" coating (not ablative) and I'm sure it costs a few KT. That would also show up as lost RPM.

I think the throttle cable is a solid core, not stranded. So I wouldn't count on stretch to be the problem, but it could still be out of adjustment or something wrong in Control Box or Shift Plate.
 
FWIW - If the bottom paint is on tight and in god shape it will have little to no affect on the drag or boats speed.
In many cases adding a tight coat of bottom paint will decrease drag compared to a waxed smooth bottom but you will only see the small result on a very fast moving boat. I have seen this myself with a couple of light fast RIBS I have owned which had both smooth and painted hulls over their life.
 
E80 Wow, Had no idea this was available. sure would be nice to settle the fuel question before storing it.. In my area some stations (wawa) have no ethanol fuel.
 
Mikee..... Do they not sell damn near real gas in your area? The engine you have was never designed to run above E10. I have 2007's in my boat and Merc is very explicit on this fact to the point of warranties being voided. I'm not a petrol engineer, but I know from Army fuel experts I work with daily, ethanol does indeed affect performance and parts longevity.

Beyond the engine, you are dealing with fuel hose deterioration as well as the destruction of any rubber parts not ethanol resistant in the fuel system.

Please be careful.
 
Mikee..... Do they not sell damn near real gas in your area? The engine you have was never designed to run above E10. I have 2007's in my boat and Merc is very explicit on this fact to the point of warranties being voided. I'm not a petrol engineer, but I know from Army fuel experts I work with daily, ethanol does indeed affect performance and parts longevity.

Beyond the engine, you are dealing with fuel hose deterioration as well as the destruction of any rubber parts not ethanol resistant in the fuel system.

Please be careful.
 
quote:
Originally posted by MikeeH

Short answer....No. Would E85 make that big of a difference?

Click to expand...


Could you clarify what you really meant here?

E85 is 85% ethanol and 15% straight gas .
Did you mean the much more common E10 .... or even E15 ( which should NOT be used in boats according to most every marine engine mfgr. )?? And certainly not E85.
 
I think he means E10 as that is what is common in MD. He can get ethanol-free but he's got to drive a bit to get it as he lives too close to Philly & Baltimore (it is an EPA thing around large cities from what I understand).
 
Bottom paint will slow you down quite a bit. Find a online prop calculator, plug in the numbers and see what your current prop slip is. There is one on a company site called Bblades plus others if you Google it. Water conditions, temperature, wind etc can also negatively affect your RPMs.
 
"Bottom paint will slow you down quite a bit"

Tight well adhered bottom paint forms less water resistance than a smooth waxed hull. I have direct experience where I gained a little over 2% speed (about 1.5 knots) on a larger RIB with the single variable being the bottom paint added. It is due to the same reason golf balls have limits on the number of dimples allowed or why sharkskin really has great texture when viewed up close - less drag.
The affect is minor until you get to higher speeds beginning at about 40 mph but it exists all along the chart - so in this case it is likely nil unless the paint is in poor shape.
You can find more information on the affect of hull surfaces on speed by searching in forums where offshore race boats and higher speed hulls are common.
 
The bottom paint is in poor shape and I wasn't planning on repainting it since I keep the boat on a jet dock. I guess I need to rethink that. It's an ablative so maybe I can wear it down :). As to the fuel, I meant to say 10% ethanol (really loosing my mind with these fuel options) but then I went to fuel the car last night at the same station I fueled the boat and paid particular attention to the labeling on the pump....no notations about ethanol content the I could find. I was going to go inside to ask but was pressed for time.
 
Smitty, I have belonged and participated on a number of high performance/offshore forums for 18 plus years and have never read where any bottom paint, sound or not was a plus. I have read numerous posts where the bottom paint was removed and the boat gained speed and RPMs. With that said, I would guess that on a slower non performance hull the difference would be less and that sound bottom paint is better then unsound.
 
"have never read where any bottom paint, sound or not was a plus. I have read numerous posts where the bottom paint was removed and the boat gained speed and RPMs"

I googled marine waxed hulls and speed and got a bunch of hits here is the first two not necessarily the best or worst of that list....

http://forums.offshoreelectrics.com/showthread.php?46582-Does-Waxing-a-boat-hull-increase-speed

http://www.wmi.org/bassfish/bassboard/boats_motors/message.html?message_id=158450

On the boat that I had previously polished and waxes to a great finish I needed to change it out to bottom paint for a few days storage at times. Since I had a very good set of recorded historical data om many speed tests with the new props I decided to repeat the runs with the newly painted boats bottom. I was a bit surprised that the speed increased until I searched the same topic a few years ago when this took place. I believe that MikeeH has indicated his situation is different due to his condition of the hull but this concept might helps someone else in the future chasing down speed issues.
Here is s picture of the hull on the faster RIB prior to bottom paint....

 
I have the 2007 version of that runabout. I run a three bladed 21 pitch aluminum prop from Solas. I can get to the upper rpm range by working the tilt. I can get 46-49 mph via GPS with two people and 3/4 full gas tank. I would say that it is your prop.
 
Was the outdrive trimmed up slightly when you were at WOT ? You will not achieve max speed / RPM with the bow of the boat buried in the water.
 
Boat was trimmed. I do have access to an aluminum p21 as well as the SS p19. I'm going to hang the p21 first and see what that does.
 
Mike, don't overlook the ethanol issue. I go out of my way to buy "real" gas as it runs better by at least a knot on my power cat. I learned that with our trips to Florida where Rec 90 is readily available. Tried it back in MD with same results. Fuel lasts much longer too.
 
Kurt,
I checked the pumps where I often get gas and where I filled the boat tank. I see no notice of ethanol content at all. I had assumed it was E gas but the pumps aren't labeled as such so maybe.....
Before you ask, no, I didn't go into the store there and ask about it. My bad.
 
Mike,
As far as fuel goes, my 2004 Silverton with Crusader motors and electronic ignition ran and performed the same on all aspects whether i used regular fuel, mid grade or high test. I was told, the electronic ignition adjusted for the different octane levels. I assume mercury with electronic ignition is the same.But just for the heck of it, next fuel put in high test. SS prop will give you better performance because they don't flex like aluminum. The downside to SS is if you hit something, with aluminum, the prop absorbs more, with SS, the gear case absorbs more of the hit.

PS

enjoy the new boat, great function fun day boat!
 
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