After the success of the 4 blade prop trials on my 685, my mate who helped me with those trials decided he had to try one on his 625 CruiseCraft – now it was my turn to hang on & write numbers down at the same time! His rig is an Outsider with a Yam F200 4/, so max hp and a fairly hefty weight on the transom. A few have showed interest in the 625 results so I have posted in a separate thread.
His current prop was a Saltwater 15 ¼ x 17 ‘M’, which revved to 6k at normal trim with 2 POB and ~½ - ¾ tank. SOLAS suggested one of their 14 ¼ x 17” 4 blade props should be pretty good, as the next size down was a 15”p so most likely too small at that diam. A 16”p would have been nice to try too, but none were available.
We conducted the trials off Manly from ~ high tide (07:45) on Sat 31st Oct, and you couldn’t have asked for a better day to conduct prop trials, as even writing down data at WOT was easy as it was pretty much a glass-out with maybe 5kn ~SW-S.
Prop particulars (in order of trial) as follows:
Trial 1 - 3 blade Yamaha 15 ¼” x 17”p Saltwater ‘M’ series (existing prop)
Trial 2 - 4 blade SOLAS 14 ¼” x 17”p
NB. The 4 blade is a full inch smaller in diam. The ‘M’ series is pretty common for Yam 2 & 4/’s up to 200hp, hence a lot of you may have the same prop. I have/had the ‘T’ series, which is for 250hp donks & up, however I have heard there are a few with 250’s running M’s.
Reciprocal runs were conducted pretty much E-W and averages were taken, however with such good conditions and not much tide run, the largest variation (in opposite direction) was ~1km/h SOG, with most within 0.5km/h, and a lot less, hence pretty close/good data.
How did the 4 blade go? Well pretty bloody good really, as the results show... AND...the donk needs to come up one hole with the 4 blade (maybe more, currently @ 2nd hole up from lowest). Therefore it can only get better! Obviously there was no lumpy stuff anywhere to test the rough water performance, so I can’t comment on this, but she felt like she would have the same benefits I found with mine, as the transom lift was quite noticeable, and the extra grip and acceleration were fantastic.
To comment on the same points as previously (from Merc site)
Four blade propellers usually:
1. Plane the boat faster than 3-blade propellers – YES, considerably
2. Keep the boat on plane at a lower speed – YES, by 3 – 4 kmh (lower plane speed)
3. Give improved mid-range speed at the same RPM as a 3-blade propeller – above 3500 YES, but b/w 28 - 35 slower, refer graphs
4. Provide quicker acceleration than most 3-blade propellers – YES, definitely, across all revs
5. Run smoother than 3-blade propellers – Not tested in rough waters,
6. Have better holding power in rough conditions – Not tested in rough waters,
7. Are less likely to ventilate in sharp turns – YES, nil evident, but motor 1 hole too low,
8. Provide better low speed handling – in the smooth, YES, should also be better in the rough
9. Are not quite as fast on the top end as a comparable* 3-blade propeller – NO, significantly faster, refer graphs
Note:
* if they mean by comparable – ‘achieving the same revs’, well pretty much so, or at least it should after the donk is lifted.
One thing I didn’t comment on previously with the 4 blade props (685 thread) was the extra grip around idle/low revs & for manoeuvring at low speed. This is very noticeable, and it is a lot easier for close quarter manoeuvring round the marina & spinning the boat etc. The 625 was also a lot quicker at idle with the 4 blade, although this could be a disadvantage if you do a lot of livebaiting at really slow speeds etc.
Speed comparison
What most blew us away was the extra speed – a pretty constant 5 - 6kmh SOG from 4500 & above. At the same ‘normal’ motor trim (as the 3 blade, between 3 – 4 bars) the 4 blade was only revving to 5700rpm, however as mentioned the anti-vent plate is buried and needs to come up one hole (or more??) which should pull the revs back up to around 5900, and mean this prop should be spot-on. How low was the donk?...well tight turns at 5000rpm with normal trim and the only ventilation we got with the 4 blade was me...hyper-ventilating while trying to hang the f@&# on!(it’s a lot easier with a wheel in front of you).
The reason for all this extra speed was only evident when I entered all the data into the PC, and if you have already peeked at the SOG graph you would know – it is not physically possible to get as low as 0.5% slip, let alone 5%, so the 4 blade is not a 17”p but probably somewhere around 18.2 – 18.5” true pitch, and at this pitch therefore would be around 8 - 8.5% slip. The 3 blade ran down to ~9%, which falls in at the lower end of the minimum slip range for 3 blades as suggested by the experts, so one must assume it is about spot on at 17”p.
With the extra grip from the 4 blade you could obviously trim out much further, where she was faster again, and we got over 76k’s on the GPS. The 3 blade could get nowhere near this!
Consumption/Economy
My mates eyes really lit up when the Yammy economy gauge hit 1.7km/L with the 4 blade, which is pretty good for a decent size GRP boat with 200hp! In the lower range of the trial revs the economy was a tad worse, but between 34 and 5500 it was mostly better, if not the same. Contrary to the trials on my boat this 4 blade chewed more fuel over most of the trial range, however with the extra speed more than compensated, hence the economy was better for most of the range.
What does all this mean? Well, on paper and by feel on the day, it all looks pretty good. ROUND 2 will come after the donk is raised, repeat data is taken (and we will also trial my 18” 4 blade just for comparison), and it gets a good test offshore in the lumpy stuff. I’ll then add the new data to these graphs & the comparisons should be interesting.
In the meantime, there are dozens of 625’s Explorers and Outsiders around on Ausfish, with all sorts of donks & props, so let’s get some comparative data! You don’t have to go to this detail, just note some data at the sweet spot and over a few different revs to WOT, & both directions too for a good average.
Cheers
Brendon
Hi Brendon
Well done and very interesting!
How do you reckon one would go with 4s of some description ? on a twin 115HP Evinrudes riggged Vagabond (similar to the 625?) that at present has 13.5 by 20p Rakers on it?
Also running foils and tabs with the foils above water from med cruise to high speed running with 40+ kn topspeed at about 5200rpm.
Cheers
Chimo
What could go wrong.......................
Hi Chimo,
Mate I’m no expert but started searching for info over a year ago even before I got my boat. From my research on the US sites etc we are way behind in thinking, experience and pure marketing over here with 4 blade props. Well except for SOLAS that is, who are obviously on a good wicket as no one else seems or wants to bother! They seem to have a pretty good range now across the hp sizes too, and a lot more than this time last year.
It seemed that most of the fishing/offshore boats or serious users over there all ran 4 blades (some even 5!), and those that had tried them would never go back to a 3! And we’re talking twins as standard set-ups & tri outboards not too uncommon. Twins with 4 blades had people raving on the handling benefits.
When setting up your boat/donk they even ask if you will run 3 or 4 blade props as they automatically set the donks one hole up if your running 4’s. There are heaps of brand choices too, in both ally and SS. (you could try the Evinrude forum on iboats)
Running foils you are obviously looking for extra lift at low cruise speeds, and you would certainly get that with twin 4 blades. Not sure how many size variants are available locally for your size (around that diameter too), but I would try & get my hands on some smaller diam (high 13’s or very low 14’s) in 18 or 19p. (check manual for max recommended prop diam). As a guess your donks would be rated b/w 5 – 5500 WOT hence if I were to take stab I would say 18’s – but try as many as you can get a hold of. Give Steve a call, I think he’s the only one in Oz that knows what he is talking about, and stocks them!
If you do try some it would be interesting to hear of the results.
cheers
PS. On my last boat (Q610 + 140 white suzy) I messed around with props & engine hts. Had a permatrim and tabs and with a good 3 bl prop, got it up 2 holes from original setup but still wanted more transom lift & better handling. The guy I sold it to put a 4 bl on it & said the difference was amazing.
Anyone with a white donk on a CC, or any boat for that matter, and is thinking about a 4 blade should check this prop out. Came across this one on ebay, which is the same prop as the one I tested on the 625 mentioned in this thread, except it will only suit V4 – V6 OMC/Bombardier donks (not the 4 stroke white zukes). Looks in great nick, and pretty cheap too.
Cheers
Brendon
PS. No relation or connection to the seller whatsoever. If it would fit my donk I would buy it just to try it, as I could probably sell it for the same money anyway me thinks.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=120545747137&ssPageNam e=STRK:MEWAX:IT
PSS. Re. my post at the start of this thread, the donk has come up one hole, and the boat is performing better for it, but we have not had the time or weather to re-conduct trials & compare. One day....
gofishin
I totally agree with everything you say about 4 blade props,i would never have a 3 blade again.
As for buying one and pricing i checked out the fleabay one and for US $400.00 delivered USPS Priority 7-10 days you can buy a Solas 4 blade Titan solid/fixed hub or the Rubex 4 interchangeable type hub system.
For the life of me i can't work it out,3 step distribution o/seas price delivered about 55% of the local price buying direct.
Hopefully did not digress too much,your post after all and you should be congratulated for your efforts and taking the time to share it with us all.
Steeler
DoNotFeedTheTrollsAandBelligerent
thanks to all on your info , very interesting re the 4 blade filling my empty head with alot of GOOD info.
what i am amazed about is the fuel economy with such big motors as the last boat i had was an arvor , great boat but just not quick enough and not enough to sit on the back of a wave . but hey GREAT boat.
it's just on your figures the gap ain't that much for the extra speed...
do we have any comparisons (unbiased between etec and 4 strokes re fuel enonomy 175 or 200 . thinking for a 20 bertram.
thanks to all above for your help.....pat
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