CONTINUOUSWAVE

I'm seeking advice regarding propeller selection for my 1989 Boston Whaler 25 Outrage with twin 2004 Evinrude 250-HP direct-injection engines.

I am now running Hydromotive q-IV 15.5 x 24-pitch propellers; these are way too heavy for my application and engine mounting height. Due to EMM failure last season I don't have exact numbers with these propellers, but if I remember correctly engine speed was approximately wot at 4,400-RPM and boat speed was 45-nautical-miles-per-hour trimmed out. The engines are 25-inch shaft models and are mounted on brackets to get closer to the optimal mounting height. But they are probably still mounted a little too low. I could probably lift them 1-inch to 1.5-inches more on the lift, but I'm a little worried about the extra stress this puts on the transom.

The boat is a little stern heavy, so I plan on installing a 45-gallon freshwater tank under deck in front of the console. Both for adjustable ballast, but also for freshwater rinsing after fishing.

What propellers would you recommend for this application?

I can get a set of 22-pitch BRAVO-1 propellers for a fair price. My goal is to increase tull-throttle engine speed to reach the recommended RPM for my engines and good cruise speed. Top speed is not very important, but would think close to 50-nautical-miles-per-hour , should be within reach.

If your recollection of only 4,400-RPM engine speed at full-throttle is accurate, the engines are about 1,000-RPM below where you should be aiming. Figuring a 2-inch change in pitch will give about 400 to 500-RPM change in engine speed, an old rule of thumb, then you ought to reduce pitch by 4-inches. Since you have 24-pitch propeller now, the rule of thumb suggests trying 20-pitch.

Are the engines a combination of standard and counter rotation? It can be hard to find sets of LH and RH propellers that you can test without buying.

In addition to prop pitch, you need to pay attention to the diameter, the brand and model of prop AND engine mounting height.

While not an expert, a Bravo prop are associated with sterndrives. I would contact a Evinrude dealer that has prop experience who can give you recommendations.

As for engine mounting height, the recommendation for Boston Whaler hulls is for the engines anti-cavitation plates to be 1 1/2-2" above the keel, assuming no setback.

Thank you for your answers. I follow you on the rule of thumb, but heard that's only applicable when comparing propellers from the same brand and model? My hydromotive looks to be very close to a typical surface prop, which would be extra heavy to run when mounted deep. I guess my hope was that the bravo 1 would like to be mounted deeper then my hydromotive. Also read on different forums that my props are underrated regarding pitch? And the bravo 1's are overrated by approximately 1 inch? And that this combination would give me the desired rpm?

From my calculations a 22p propeller at 5600rpm, with a 1.86 gearcase and 10% slip would give me approximately 49 knots. Is this speed within reach on this hull and engine combination or am I being to optimistic regarding the speed potential of this hull and engine combination?

I have been looking at rx4 18-20p and rev4 19p, this would probably be the best solution, but these would have to be imported from the states and cost 3-4 times more then the used Bravo's that are for sale here in Norway. The prop market for twin installations fast offshore fishing boats are close to non existing here. I have seen two sets for sale during the last year, both were 22p.

My engines are a combination of standard and counter rotation and a set of test propellers are unfortunately impossible to get here.

BW -

Sorry - I would have given a bit different advice had I known you are in Norway.

When running a prop calculator note that most of the Whaler prop gurus I know use 5% for slip.

What other brand of props are readily available? Are you near a major city like Oslo or Bergen with many dealers?

Re the speed potential for an OUTRAGE 25 with 500-HP, I would think 50-nautical-miles-per-hour or 57.5-MPH would be in reach without much trouble, as long as the total weight was not excessive. But you probably wouldn't like the ride in any sort of open water at that speed.

Since you have one standard-rotation engine, maybe you can borrow one RH propeller and fit it on that engine, just to see what sort of RPM it will turn with a pitch change.

Thank you both for replying. I was recommended to contact Ken from Propgods, which I did. He replied quick and precise and strongly recommended the 22p Bravo's and lift the engines. So I bought those Bravo's for a very fair price and can't wait to test them. Hopefully the snow and ice have melted for the Easter break, and I'll try to do a proper sea trial then. If you are interested, I'll keep you updated and upload some pictures?

Thanks again!

Bw25 wrote:I was recommended to contact Ken from Propgods

Ken has helped me as well, good luck with yours and share the results--and photos of your boat, of course.

Update?

With jackplates you can keep raising the engines until you go too high then lower them a 1/2inch. You will put more stress on the transom going deeper than if you raise them....hence the low speed due to drag which means stress.

Hi, sorry for the late utdate. Due to some problems and very busy at work, this season has started very slow and late. I raised the motors all the way up (might have to lower it a bit since it looses grip when going on plane and in hard turns). Cavitation plates are dry on the outside and gets little splashing on the inboard side. The new bravo 1 22p helped, but I'm still not getting the rpms I would like. I'm now getting 49-50 knots on gps, but only 5100-5200 rpms with light load. This seems like very good slip numbers and definitely much better then I was told to expect from Bravo 1 props. I'm happy with the speed, but would like to be closer to 6000 rpms with light load. Acceleration is very good. I'm gonna do a decarb and change plugs, but I'm afraid this isn't enough. Plugs are almost new, but don't know when it was decarbed last time.

Some pictures.

Don't know why the first picture ended up stretched and I don't know how to reduce picture size on iPad, which I needed for uploading here. Will try to upload some more pictures tomorrow.

Best regards Adrian

Before I offer additional advice, answer me this.

What will be your typical load (fuel, passengers, gear)? What are your typical ocean or lake conditions?

Typical load is 1/4-1/2 tank of fuel, 2 persons and approximately 250-300kg of gear, ice and ballast. Sometimes up to 8 persons and I plan to build a t-top for next season. Ocean conditions are mostly protected and less then 0,5m significant wave height. Longest trips are 110 nautical miles, but most trips are much shorter.