Mercury Props.-

[Faztbullet]

The picture you posted is a Bigfoot or what they call Command Thrust unit using the 13-14" diam props, a standard unit uses a max 12' diameter. Need to drop it in diameter not pitch....

 

[QBhoy]

The above explains it. It is indeed a Bigfoot and big Diameter prop to counter.
I’m sure I asked this in my first post.

 

[QBhoy]

If it’s not a Bigfoot, then it’s certainly a big unusual diameter prop from one.

 

[Sea Rider]

OK will post new prop shots to determine 100% if being a Bigfoot ot not, will ask the Merc seller who sold the motor if that 60 HP is the Bigfoot version or not which btw was delivered factory propped with a Black Diamond 11 starter pitch, same as the rest 3 motors in stock.

What don't want is to try different brand props and models which will definitely turn into a very costly experiment which it's my friend's money. We rather prefer to invest the money wisely in many cold ones..

Found this prop info which states : Diameter is the width of the circle that the prop would make when rotating. The diameter can vary by up to 1/2" with no discernable change in performance. So who's right ?

Happy Boating

 

[racerone]

Operation of tachometer has been checked / calibrated ??-----Something is wrong on this boat motor combo !!

 

[Faztbullet]

No need to post new pic's of lower unit...the prop part number and housing design confirms it....Also dropping 1' in diameter will raise RPM by about 500RPM

btw was delivered factory propped with a Black Diamond 11 starter pitch, same as the rest 3 motors in stock.​

Must be something different in your country as the Merc website plainly states motors come with no props or controls unless a tiller model and that comes with no prop.

 

[Faztbullet]

Heres how the 60 EFI come in the box from Merc….

 

[QBhoy]

If it’s not a big foot, it certainly has an abnormal large diameter prop on it, typically found on a big foot.
can usually tell by it having a larger than normal gearbox on it. Will usually say it on true engine hood too.
they were called big foot up until about 2015ish. Then called a CT or command thrust.

so for example a I have a CT 115 merc. It has the larger gearbox similar to the bigger 150-300ish motors. Takes the larger props too. The normal 115 has a smaller gearbox and a higher gear ratio.
The idea is that the motor can give more thrust low down when pushing a larger and heavier hull that usual. Not ideally suited to a small rib, but you can offset it with changing props.

 

[Sea Rider]

Checked the motor's cowl, it's definitely a Bigfoot 2006 year model. Was reading that this type of motor with taller and larger lower leg is best suited for toons, water houses, barges applications not Ribs. There are no Black Diamond props with less diam in the 11 pitch model which are 10-7/8. Diam is what the prop manufacturer wants to build his props with, pitch is all what matters.

Saw at the Merc store a brand new 4 stroke 60 HP GT Command Thrust model, specs states being a 2:33:1 gear case ratio, asume that the Bigfoot 60 has a different ratio, right ?

As the motor has very low hours of use, assume that the tach is in good working order. Probably impossible to check it with another one, but will like to measure its Top speed with a GPS in a long run.

According to IBoats web page information Diameter is the width of the circle that the prop would make when rotating.



The diameter can vary by up to 1/2" with no Discernable Change in Performance. So what's your idea about it ?

Happy Boating

 

[QBhoy]

Checked the motor's cowl, it's definitely a Bigfoot 2006 year model. Was reading that this type of motor with taller and larger lower leg is best suited for toons, water houses, barges applications not Ribs. There are no Black Diamond props with less diam in the 11 pitch model which are 10-7/8. Diam is what the prop manufacturer wants to build his props with, pitch is all what matters.

Saw at the Merc store a brand new 4 stroke 60 HP GT Command Thrust model, specs states being a 2:33:1 gear case ratio, asume that the Bigfoot 60 has a different ratio, right ?

As the motor has very low hours of use, assume that the tach is in good working order. Probably impossible to check it with another one, but will like to measure its Top speed with a GPS in a long run.

According to IBoats web page information Diameter is the width of the circle that the prop would make when rotating.



The diameter can vary by up to 1/2" with no Discernable Change in Performance. So what's your idea about it ?

Happy Boating

Hi again Searider. We are getting to the bottom of it here. Great stuff.
so as far as I know, with out checking, the 60hp Bigfoot will have the same gearbox and prop fitting (but not necessarily same ratio) as a similar aged model from about 75-125hp. So the likes of a prop typically found on a 90hp merc attached to a 15/16ft speedboat) would fit it. Just worth a double check perhaps. But the typical prop found on such a set up would be something like a 13x17 or 13x19. As in 13” diameter and 17 or 19” pitch. Much smaller diameter than what is on now.
so given the engine is a smaller 60hp (but Bigfoot) you’ll likely be good to try something similar but if a lesser pitch like 15”.
Have a wee look online for black max props. Even just a quick look on eBay there shows a range of props available and some even say suitable for “75-125hp and smaller hp Bigfoot models”

 

[Faztbullet]

From Mercury Marine..

"Within a specific propeller style, diameter is usually larger on slower boats and smaller on faster boats. Similarly, for engines with a lower maximum engine speed (or with more gear reduction), diameter will tend to be larger. Also, diameter typically decreases as propeller blade surface areas increase (for the same engine power and rpm)" With several thousand hours under my belt on performance boating have seen just about all types of prop/engine misuse. Find a smaller diameter and try it...you maybe surprised.​

 

[Sea Rider]

Finding a less diam prop with same 11 pitch will be more difficult than finding a needle in a haystack, that's for sure. So you guys don't think that by going for say 2 less in pitch with much less diameter will do the trick ? Need to bump max wot rpm to 6 K lightly loaded with 2 or 3 max up.

Happy Boating

 

[QBhoy]

Finding a less diam prop with same 11 pitch will be more difficult than finding a needle in a haystack, that's for sure. So you guys don't think that by going for say 2 less in pitch with much less diameter will do the trick ? Need to bump max wot rpm to 6 K lightly loaded with 2 or 3 max up.

Happy Boating

I’d still say don’t go lower than 11”p at all. But certainly need to lower the diameter.
I’d still also do a compression check to rule anything nasty out. Apologies that’s been done already.
It’s definitely behaving strangely

 

[Faztbullet]

The issue with this 470 Rib is that the hull is nearly 20 years old, develops a tremendous front hull drag due to its odd shape when on plane at speed. Would say it's worse than a dog when running. Splashes too much water at side of front hull which slows the combo real bad.​

If this is correct a prop change to a 9" will get a extra 5-600RPM but will slow the speed down about 2-3 MPH .The Bigfoot or CT unit do not like being run deep and prop needs to surface a tad. If I had it at my shop I would loose the Doelfin which increases drag if not running on surface, and raise motor1 hole on transom.

 

[Sea Rider]

The easiest and fastest way will be going for same model prop with a 9 pitch and check what dials, definitely much higher wot rpm than now. Today is the wot water test, will test it with 3 up and I'll check what's going on at back transom having a look there....will report findings...Not an issue achieving bit less wot speed, this ain't a speed machine, it's a water transport..

Is it possible that this motor has a 2:33:1 gear case ratio or could it be a 1:83:1 one ? where can I find that info ?

Happy Boating

 

[QBhoy]

If this is correct a prop change to a 9" will get a extra 5-600RPM but will slow the speed down about 2-3 MPH .The Bigfoot or CT unit do not like being run deep and prop needs to surface a tad. If I had it at my shop I would loose the Doelfin which increases drag if not running on surface, and raise motor1 hole on transom.

Said the same from the start, about the foil. I think searider said it’s now off the engine. if it isn’t, it should be.
searider, this Rib with a conventional set up 60hp should achieve into the 30’s gps....very easily. All being well.

 

[Sea Rider]

Updates :

Tested the combo with 3 up on flat calm water cond, at full 5K wot revs while riding at neutral trim, this is what was found :

1-Water flow is passing parallel about 10 mm under the upper splash plate (red line)



2- Doel fin rides parallel to water surface while it's not exposed which is good. Useless going one up hole, the plates distance is short besides being too much hassle.

Personally would prefer for water flow to skim right under the upper plate¡s lip (yellow line) same height dialed on all my friend's including my personal Rib. For that will need to chop transom down a bit as the motor sits even on transom as of right now.

3-Compared to a modern Rib hull (2) the old hull (1) produces excessive water drag, requires a tad larger HP motor to equate an equivalent same size Rib that uses a less HP motor.






4-Last but not least, guess what ? The control box although throttles to max range, the motor wasn't doing so. The motor was badly cable adjusted, needs about 15 mm adjustment to run at max wot range, definitely a shade three mechanic installed the motor...

5-After a correct throttle box/motor adjustment will make another water test and check if at least runs at min 5500 wot rpm, the extra missing 500 wot rpm can be compensated going for same style 10 inch prop as a second starter prop which is readyly available...

Happy Boating

 

[WesNewell]

I guess you'll never get it, but the lower plate (AV plate) is what needs to be above the waterline at wot plane to get maximum performance and fuel efficiency.

 

[Sea Rider]

Nope, in this precise example if the AV plate rides above the water level which is ridiculous or under what's the use of the doel fin, that I know a doel fin must ride fully submerged and parallel to the water level to work right, unless you want to use it as a step lader when climbing on board from behind...

Touche, you'll never get it right on your side as you have not tested that setting on all water cond, that's from flat calm water to choopy ones including sharp turns at speed. That setting is only good for straight water courses at speed on flat calm water cond.

If wanting to increase performance there's nothing that a correct prop maximization will not cure when more wot revs are required. A motor running with AV plate set that low won't achieve maximum water performance worse top fuel efficiency. Fo that you need a motor well propped running towards it's max wot rpm range, once there, you can throttle at 3/4 to achieve best fuel economy, so don't tell me stories mate...

Happy Boating

 

[QBhoy]

Hi searider

Always respect your input, posts and opinion, but on this occasion you have it a little wrong. The chap who most recently responded has is right. That set up will never be optimised fully until the lower plate is running on or slightly above the surface. It should never need a doelfin either. It’s certainly have a detrimental effect to the whole attitude of the boat, the way it’s set up currently.
Hope you get it sorted out though. All the best.