1992 2520 sport cabin twin yamaha 150s economy and speed

[panga]

I am wondering what the rest of you get with this setup, my motors are brand new, I think I am getting around 2mpg, and my WOT speed is around 25knots. Does this sound about right, I was expecting a little more WOT speed, but not knowing any other parkers local to me I dont have any comparison. My motors are only getting up to about 4800 RPM, should I be getting about 5200? My mechanic is looking at the boat now, hopefully it is just linkeage adjustment to get the RPMs up, which should help with top speed a little.

Thanks

 

[Brent]

What are the props specs?
Are the engines mounted on the transom or bracket?
What is the mounting height (hole #)?
How many hours on the motors?

 

[panga]

I am not sure the specs, the boat is not here at home, I can check next time I am at the boat, the yamis are bracket mounted, only have about 95 hrs on them, I will look at where on the bracket they are mounted. Would raising the motors up a notch increase RPM? It seems like if my RPMs are only getting to 4800, the motor is boging or lugging, so the economy would be down as the engine is over working due to either wrong prop or too much drag from being to low? We did just install new cables and controls, so I am having the mechanic check if adjusting those can get more throttle, but I am not sure if the problem is here or in the prop/mounting? I just got the boat, and am not sure what the RPM got up to before the new controls.

 

[Brent]

the cavitation plate should be very close to the bottom of the boat. The easiest way is to make the boat on the trailer as close to level as possible --and then use a level to the bottom of the cavitation plate and with the engine at right angle to the hull

The rule of thumb for set backs is 1" higher for 1 foot set back. the engine may have to sit from one inch above to one inch below the bottom of the boat--the level is a place to start.

When running on a full plane, you like the cavitation plate to be just on the top of the water.

Lots of info on props just search on props
Your boat should fly

 

[Megabyte]

What year Yamaha 150's?
Two stroke, or four stroke?

 

[panga]

Any idea of what my top speed should be? Keep in mind that it is a Deep V? I will do a search and research what the prop specs should be, you've got me thinking now, maybe the motors are to low?

I will try that measuring method, I think the bracket is about 2 feet deep, so the cavitation plate should be 2" above the boat of the hull?


Thanks very much, I will check it out.

 

[Brent]

I dont know your boat, equipment esp prop type and specs and your use. There are several factors needed for a solution.
I would look at the motor specs and determine the rpm sweet spot for torque and gas consumption, and top rpm. WOT speed is important if you spent a lot of time traveling at top speed. Realistically what percentage of the time will this occur? Motor position has been discussed. Do you have trim tabs? Which brand and size? Do you travel very far away off-shore? Is speed more important than the ride? Will your boat be heavy with passengers, gear and ice coolers for food, bait and fish? Is it important now to purchase 2 high end 4 blade high performance SS props? It is a lot of money if you dont consider all of the factors. I still think the archives has the best information then you decide what is best for you. Nearly everyone has a succes story for their boat which may or may not be effective on yours. When searching, start saving links and print topics and store in a 3 ring binder.

 

[panga]

Thanks for the tips, tomorrow I will go down to the boat and have a look at the motor height, and check the prop specs. I will continue checking the archives for prop info on this boat and motor combination. So far I have not found anything specific for twin 150s and a 2520 deep v. I do often run off shore for tuna 40-60 miles. In these situations I am not looking to run at WOT, but run at a moderate cruise speed and get the best economy possible. The last few runs, with a full tank of gas and some ice and 3 fishermen I am running at about 20 knots and burning over 16GPH. I do have tabs, size by memory would guess about 6"X14". Fuel economy is my priority, as ocean conditions here in the pacific northwest rarely allow one to run wide open off shore, but it does happen occasionally, and it is nice to be able to get to the grounds in a hurry when the opportunity presents itself. It seems like I should be getting better economy then I am, but I am not sure? I will check the engine height tomorrow and report back.

Thanks for the help, much appreciated.

 

[BradV]

If the 150s are 4 stroke you need to be spinning them close to 6000. You should have a 17 pitch prop on that thing and preferably a Rev 4. Cruise should be about 24-30 Mph and you should be turning 3700-4500 RPM and getting 1.5mpg -1.7mpg loaded up. If you are light you could see a little close to 2.0mpg but for the most part i wouldnt count on it especially if it picks up. 6 x 14 tabs dont sound right but maybe. If you can swap to a 14 x 18 or 12 x 16 that would help.

 

[Megabyte]

Brad is correct. 4-strokes should be turning around 6000 at WOT and 2-strokes should be turning 5500 at WOT.

As for tabs, go for the widest you can install without clearance issues. I have a single motor on my 2520 MV and my tabs are 24x9 Bennetts, but we have at least one member who installed 30x12's on his 2520 MV.

Bennett Marine can assist with the selection process. Simply PM member Tabman and Tom can assist you.

 

[Brent]

I plan to test various props someday and contacted Ken at Prop Gods in FL when I bought a spare non high performance prop. They have a mobile prop testing service so you can try various props and test on the water
Their web site is http://www.propgods.com/Content2/Online ... fault.aspx
They have a prop forum at http://www.propgods.com/forum/ but m2cw is Brad V and Megabyte presented the best advice.

There might be a mobile prop company or prop exchange in your area. What an incredible service to us

 

[DaleH]

FWIW my bro runs twin Yam 150hp old 2-strokes on his 23' deep-V Grady White and his fuel economy is better than 2mpg @ 3800 RPMs. His max RPMs are 6K per engine and he turns 5800 in the Spring in cool air with freshly painted bottom. Yams LOVE to turn near max RPMs.

 

[panga]

Yeah, I think my bottom may be adding drag also, not in the best of shape, def causing some drag. Im off to the boat now to check the props and engine height out.

 

[DaleH]

It is my humble opinion that 99% of the factory or dealer mounted OBs are mounted WAY too deep on the transom ...

 

[panga]

Just back from boat, prop is a 17 pitch and the motors are mounted at what appears to be the correct position on the bracket, about 2.75 from the bottom of the boat to the cav plate. My mechanic is doing some adjusting with the control cables, as they were recently replaced and reconfigured, and with twin engine dual station it takes some tweaking. We are thinking the control cables are not opening the throttles entirely. Hopefully this will do it, and get me some more top end and RPM. My bottom is definitely contributing to the problem, it is far from smooth, this should be repaired after fishing season.

 

[panga]

Just ran the boat for 1st time since getting it back from mechanic. He adjusted the linkage, and we are definitely getting WOT at the engines. I am getting about 5000RPM now, and running about 25knots with 4guys, half tank fuel, and 8 bags ice. I dont really have a problem with 25knots, I am just worried that if I am only able to turn 5000 rpm I may be damaging the engines by lugging them? What do you think, should I try different prop. The engines are definitely mounted plenty high, any higher the props would slip in rough seas. Any advise?

Thanks

 

[Brent]

What is the condition of hull?
Does it have a full beard and need new bottom paint
If me and with the above advice and their voice of experience, I would buy new props
Which hole is the engine mounted?

 

[panga]

Hull could use new bottom paint for sure, it is not terrible, there are a good amount of "worm shells" (for lack of better describing word, white worm like empty shell about a millimeter in diameter and an inch long) from the previous owner who had it in the water in southern california. I am waiting until after fishing season to deal with the bottom. But.. again it is not terrible just not supper slick. Nothing alive, no moss or algae or muscles, just the remnants of these white worms? I guess props it will be. I cant recall which hole they are mounted on, but I do know that in some really rough water today I had to keep the motor trimmed down to keep the props from occasionally spinning out when dropping off a big wave? So if they were mounted any higher I think ventilation would be an issue.

Thanks for the help,

 

[Brent]

welcome
Can you post some pics?

 

[Megabyte]

5000 rpm isn't exactly lugging it, but if they are 2 strokes, 5500 is closer to where you need to be.
Can you swap those 17p props for a set of 15 or 16p's with a local prop shop?
It would be interesting to see the difference it would make.

Don't want to go too small as low and mid-range could suffer, but it would be a good test of the top end.
If a 4-blade, I would think 15p.