Twin Yamaha 150F / unusual prop application

[smitty477]

I have just purchased a large used RIB with existing props that we sea trialed a couple of weeks ago. I am now in need of selecting other props and would like to ask what choices may make sense for my application. I have read a bunch about props so I likely know just enough information to get myself in trouble here but I will give it a shot anyway. My goal is to select reasonably priced SS props for all around use to include cruising, and towing skiers with 2-6 people on board. At sea trial the engines pinned the tachs quite easily with a 2-3 foot chop, strong wind, in salt water and 5 people on board (adults). The boat held plane easily at 30mph @ 3,800 rpm?s as well as at lower speeds

Boat is a 2010 Nautica RIB , Catamaran (shallow hulls), 23' long, 8" 6" beam (tube to tube), total weight rigged to is 3,250#'s, (hull 1,790, engines 960, fuel etc 500). The hulls are 24? apart at the bow and shallow along the length, they are asymmetric.

Current props are ?stock? Yamaha black painted SS, 3 blade 19? pitch.

Motors ? Twin 2009 Yamaha F150 4 stroke, 2.00 lower, counter rotating, in good condition, tachs are Yamaha digital. WOT range is 5,000 - 6,000.

Mounting - Mounted with jack plates and adjustable over keel range at 2nd hole static. There are no doel fins, trim tabs, or other 'things' back there.

What are my options in type and pitch of prop and what else can I do to help determine this? I have had good success with Solas props recommended here but they have many options on the site. Can I begin to select reasonable replacements at this time - and if not what do I test again when the boat is back in my hands?

Thank you

 

[BaileysBoat]

Re: Twin Yamaha 150F / unusual prop application

Not sure what you mean when you say the tachs were "pinned". If you topped out at 6000 RPM with the with 5 people aboard that is exactly where you want to be. The black painted Yamaha SS are good props. Sounds like you don't need to change a thing?

 

[smitty477]

Re: Twin Yamaha 150F / unusual prop application

"Not sure what you mean when you say the tachs were "pinned"."

Easily hitting the rev limiter causing intermittent cylinder deactivations above 6,050.
I know the boat is underpropped but I do not know which type or pitch of prop might be the best step next.
Some prop 'calcutors' call for as much as a 24" pitch set of props but that sounds like way too much.
Most all of the Yamaha perf bulletins favor the Yamaha 'Reliance' types of props.
There does not appear to be any similar perf bullitens to use as a close guide.

Again, not sure what my comparisons should/would be.

Thank you

 

[smitty477]

Re: Twin Yamaha 150F / unusual prop application

After reading some additional perf bulletins I am even more confused as there are no direct comparisons to what I have..
Since I have not replaced many outboard props at all I am not sure of which 'online' prop advice is correct since they seem to disagree much of the time.

My new questions include - I have a stern heavy boat and that often leads to a 4 blade prop. But it is also overall light with 2 engines so that leads to a 3 blade prop. Which case is correct?

Why would one Solas SS type 3 blade be preferred over another one? Or there 4 blade SS?

On the bulletins I can find the same weight V hull with a single 150 F Yamaha and 19" pitch - what happens when you double that power?

On the bulletins I can find a RIB w/twin 150F Yamaha's and 19" pitch props but at 2,500+ pounds heavier - what happens when you have that much less weight?

On the bulletins I can find a Catamaran hulls that have twin 150F and 19" pitch props but again at 2,500+ pound heavier

What is a good way to get from what I can look up about other boats and know about this boat to figure the best props for this boat?

 

[Philster]

Re: Twin Yamaha 150F / unusual prop application

21P, 4-blade props. That's what I'd try next.

It is possible 23P would work (or more), but we don't know how deep into the RPM range those engines can get to because the rev limiter obscures the info: i.e., The engines might have 6100 RPM in them with the given load, but they might have 6400. The potential is unknown because of the rev limiter.

You have enough RPM to absorb a step up in pitch PLUS adding a blade. We know that at a minimum.

(If you have power/speed to spare, no need to squeak out every MPH by sticking to 3-bladers. 4-bladers are great for lifting the stern and getting bite/handling along with hole shot and better mid-range performance)

 

[BaileysBoat]

Re: Twin Yamaha 150F / unusual prop application

21P, 4-blade props. That's what I'd try next.

(If you have power/speed to spare, no need to squeak out every MPH by sticking to 3-bladers. 4-bladers are great for lifting the stern and getting bite/handling along with hole shot and better mid-range performance)

I agree, would try a 21P. 4 blade makes sense. Can someone lend you a set for a sea trial?

Keep us in the loop.

 

[Dhadley]

Re: Twin Yamaha 150F / unusual prop application

Where are you located? I may know where you can get a pair (R & L) 14.25 x 21 Turbo Ultima 4s.

 

[smitty477]

Re: Twin Yamaha 150F / unusual prop application

Philster- thank you for your feedback. I have very little experience/knowledge of outboard props and there changes and absolutely zero when it come to two engines. So when you go to a 4 blade even when you have 2 motors I am a bit surprised since the blade area is doubled with the 2 props. Would something like a Solas Titan 4 be the a candidate?
I will not have the boat here with me for another 1-1/2 to 2 weeks but at that time I could do further testing as is (with 19" 3 blades) if it would help. Would it have any value to record the time it takes to reach a certian speed or WOT for that matter?

Baileysboat - If only I knew of a way to test by borrowing or renting that would be great.

Dhadley - I am in Northport NY about half way out on Long Island. The boat itself will not get to me for a couple of weeks as it was just purchased out of state.

When looking at the perf bulletins it seems like maybe I should pay most attention to the lightest catamarans with teh same motor combination. I am guessing that the engines do not know it is an inflatable and at all but idle speed the tubes are not going to be touching the water anyway. Does that make any sense?

Thanks again

 

[Philster]

Re: Twin Yamaha 150F / unusual prop application

Going to 4-blades is the proper luxury your power can afford. Also, consider the weight hanging on that transom: You want blade area to manage it.

I don't know much about Solas props. I know more about Mercury and Mercury Racing props. I do know that there is the Trophy from Mercury and the Bravo for Outboards from Mercury and both are 4-bladers. I would lean towards the Trophy. For hulls like yours, it would be fine.

Merc stuff ain't cheap. Maybe others can chime in on other quality brands that might be a better value.

 

[Dhadley]

Re: Twin Yamaha 150F / unusual prop application

I will be out of touch until next week (Tuesday) but I know I can arrange for you to hook up with the Turbo Ultima 4s. I'll send you a PM when I get back.

 

[smitty477]

Re: Twin Yamaha 150F / unusual prop application

Philster - thank you again , your description does make a lot of sense.
I do have a good deal of experience with inboard cruisers and turning a wrench as most always we fix our own boats and cars.
I became aware of the Solas props here on this forum about 3 years ago when it was recommended for my 1st outboard application. Since then myself and friends have used Solas props on a number of outboards (mostly Al) and a couple of jet skiis with great results.
Not being nearly an expert but having that limited experience I get the feel that Solas makes a very good product at a very good price point. Another way to say that is you can buy a better prop but it may be at 2X the price. For what we do and how we use the boat in the NE it usually just does not make sense to need the 'very best'.Besides the fact that the boat does need a good deal of 'other work' when I get it back here as well. That is why I asked about the Solas Titan 4 as the prices seem to be quite reasonble and what limited reviews I have seen are pretty good.

Dhadley - Thank you very much. I am traveling for work between tomorrow and Monday as well and likely will be offline as well.

 

[Philster]

Re: Twin Yamaha 150F / unusual prop application

Solas Titan 4B:

Certainly, the description is in line with Merc's Trophy 4B prop as for rake, cupping and other characteristics, and they are recommended for the same types of boats. So, if you trust the brand, it certainly sounds like a good fit.

Wow, with your gear ratio, RPM range, boat type and 4B props and twins, your overall throttle response will be incredible.

 

[smitty477]

Re: Twin Yamaha 150F / unusual prop application

"Solas Titan 4B:

Certainly, the description is in line with Merc's Trophy 4B prop as for rake, cupping and other characteristics, and they are recommended for the same types of boats. So, if you trust the brand, it certainly sounds like a good fit."

This is exactly what I could not understand or compare since I just have no feel for this yet. I really thank you for your educated input on this since a fully trial and error approach would be incredibly painfull if not impossible. A boating pal of mine says he can get a pair of Titan 4b's for me under $550 to my door.
First to get the boat home and do a few more tests here on Long Island where I can more fully adjust the jack plates and trim in various conditions with the 19" 3 blades. At that point there may be reason to post back some more information or perhaps not and just buy the props - unsure untill we get that far.

Yes - I would expect the throttle response to be interesting given the weight, props, effective beam at cruise, and the shallow cat assymetric hulls. We just sold a 19' Nautica V bottom with a 115 Yamaha 4 stroke and that was pretty responsive as well.

Thanks again this was quite valuable