Hi Guys,
I have my little 5.5mtr sailfish cat powered up by 2020 model DF70A Suzuki outboards. I have the standard Suzuki 13.7/8 x 15p 3 blade Aluminium props.
I am able to get the RPM up to 5600 rpm WOT when loaded up with all the gear, 300lts fuel, esky etc etc> I do have some ventilation issues in messy chop when the motors are trimmed. I can only get to about half trim in dead flat conditions.>
I recently tried some Solas 4 Blade 13.25x 15p in stainless. The props gripped better in turns, the engines felt smoother and the boat didn’t porpoise as much when trimmed. I like the extra stability they seem to provide.
I can rev to 5900 now and can trim to hit the rev limiter.
I was expecting a little more speed or more meters per litre with the 4 blade but at a given speed I have to rev faster and in turn more fuel is being used.
Im going to try a different set of props. I know it’s a bit of a black art this prop business. It has been suggested I try a 16inch pitch set of SS Props. But the additional inch is only 6.6% difference in drive.
Do you think it will be enough to at least match my speed and fuel consumption figures in getting with the 3 blade props or should I jump to 17 inch pitch first up and then come back if I need to.
I have to get some improvement in either cruise speed or fuel use at a given speed . Range is so important to me. My average fishing trip is between 220km and 360km round trip.
I rarely run the engines over 5000rpm. Most of the time Im cruising between 4100 and 4900 rpm
what are your thoughts?
Orig Suzuki Prop 3 blade 15p Solas SS 4 Blade 15p Rpm port Rpm stbd Km/l Rpm port Rpm stbd Km/l 35kph 4000 4050 1.9 4350 4300 1.79 40kph 4500 4500 1.7 5100 5200 1.33 45kph 4950 4900 1.6 5500 5550 .98 49kph 5400 5400 1.06 5800 5900 .98 51kph 5600 5600 1.03 5900 5900 1.0 55kph 5650 5700 1.11
From what yourve stated ide say your not doing too bad considering the weight loaded in your rig . that four blader seems to be doing not too bad for you..Originally Posted by Brettoh
I have simmilar issues with my 5.2 Seajay using a 17 P prop.
Went to 15P and gained more revs but at a slight cost so went back to the 17.
Run 3 & 4 Blade prop depending where im heading and the fuel conmsumption is near the same with either 3 or 4 blade prop.
Interesting to hear what others advise ??.
Hi Brettoh
I'm running a 4 blade solas on my 5.5m Cruisecraft with 150 yammie two banger. When I changed from a 3 blade alloy prop to the lower pitched 4 blade solas it really transformed the handling of the boat for the better. The 4 blade gives more lift at the back, keeps the boat on the plane at lower RPM and speed and really reduced the 'banging' in choppy conditions. RPM at WOT went up into a more desirable range however top speed came down. This is exactly what the bloke at Solas told me would happen with the 4 blade. I can't comment on the fuel consumption as I am about 10 generations behind in electronics.
You may be in a situation where you have to compromise improved boat handling characteristics at the cost of extra fuel consumption or vice versa. You've already said you noticed better grip in turns, smoother engine running and extra stability when running with the 4 bladers however this is at the cost of extra fuel consumption. My own personal decision was to choose better handling (and my comfort) with the 4 blade prop at the expense of loss of top end speed and probably more fuel. I also noticed the boat doesn't perform as well with the 4 blade prop compared to the 3 blade when tubing and skiing with family but comfort when running offshore trumped that. Now I am aged with the dinosaurs (according to grandkids) I really like being soreness free the day after a fishing trip. Also I'm too lazy to change between 3 or 4 blade props depending whether we're fishing or skiing so it's easier to just stick with the 4 blader.
Range and fuel consumption isn't an issue for me however it is for you and may be more important to you than the benefit you have found with the 4 bladers. I know I am comparing a monohull vs your twin hull but by all means try different pitched 4 blade props, you may hit a sweet spot where you decide it is all good and you get the best of both worlds. Choosing the right prop is a bit of a dark art, sometimes you just have to try different props to find the right one.
Regards
Twosheds
Are your motors set at the correct height? Don't be messing with props until you get that right. Your statement"can't trim out more than half in dead flat conditions"rings alarm bells for me.
I cant go any lower.
The boat is fitted with the right length outboards> OOOPS I see I have a typo I can trim up fully in dead flat but at normal 4000 to 4900 cruise in varying lumpy conditions the props do pull a bit of air at times. These are the 13.875" diameter 15pitch 3 blades I have had since I got the motors. The 13.25" 15pitch 4 blade props can be trimmed more.
The issue is I cant sacrifice speed or fuel. I really dont want that. It defeats the purpose of re propping. Sure the additional traction is much better with the 4 blades but I was never wanting additional traction for tight turns at speed. The reason for change and the advice given was to either go a little faster at cruise rpm and or use less fuel for a given speed in the cruise RPM range>
Im not looking for top speed. I dont want to run the engines over 4900 rpm for 3 or more hours each way to or from the reef. But if I can pick up 100mts per litre better economy I will extend my range by about 30km over the fuel carrying capacity I have .
Im still at the crossroads of 16 inch pitch or 17 inch pitch in the 4 blade.
or I wonder if there are some 3 blade ss props with different characteristics than the oem suzuki aluminium props have that can make a positive change.?
There are too many variables ugh
Per your figures the 3 blade props are achieving -3.2% prop slip at 5600rpm, so I'd stick with those
I agree here. There's also a difference between fuel consumption and comfort. In my case 3800rpm gives me the highest fuel range yet 4200 rpm generally gives me the most comfort ride apart from short chop.Per your figures the 3 blade props are achieving -3.2% prop slip at 5600rpm, so I'd stick with those
I did similar checks as you did but added range into the equation and put the lot into a graphical format. Some people can look at figures and see the pattern where as I look at it graphically and it stood out much better. I also did tests into the wind and going with the wind, against the wind gave the best results. Sell and chop can change everything.
i think you are asking a lot of 2 x 70hp. perhaps you are searching for someting thats not there to give. getting 360klms with weight out of such a small boat and hp is not a bad effort
Too much? How so.?
The prop people say the 4 blade gives
- Great stern lift & acceleration
- High rake and cupped blade design
- Powerful thrust & very smooth performance
- Increased speed & economy in the mid-range
It might be that the OEM 3 blade props offer the best performance and If they do Ill be very disappointed. Im sure there will be another style of prop out there that can offer a little more of something in the economy field.
Yes I did runs in each direction> Number are as the wife wrote them down from the information on the Simrad in instrument mode.
Orange is my preferred cruise Speed. There is a big difference. Im just trying to work out if I try the 16"pitch 4 blade or jump to the 17 "pitch
OEM Aluminium 3 blade 15P SS 4 Blade 15 P
SPEED in KPH PORT RPM STBD RPM Fuel km/l PORT RPM STBD RPM Fuel km/l 13n 2500 2450 1.5 3300 3300 13s 2200 2250 2900 2800 1.43 29n 3800 3850 1.63 4200 4200 1.6 29s 3750 3650 1.7 4150 4100 1.66 35n
4250
4200
1.7
4600
4600
1.57
35s
4000
4050
1.9
4350
4300
1.79
40n
4500
4500
1.7
5100
5200
1.33
40s
4500
4400
1.96
4750
4650
1.6
45n
4950
4900
1.6
5500
5550
.98
45s
4700
4700
1.75
5250
5300
1.2
49n 5400 5400 1.06 5800 5900 .98 49s 4900 4850 1.38 5500 5600 1.05 51n 5600 5600 1.03 5900 5900 1.0 5s5 5650 5700 1.11
Yes I have repeatedly looked at those calculators and come up with negative figures. All I can imagine is that the cupping on these OEM props somehow changes the pitch to move more water.Per your figures the 3 blade props are achieving -3.2% prop slip at 5600rpm, so I'd stick with those
Solas up the sunshine coast will cup your prop some more & it can make a grate difrance to the performanc
- [COLOR=var(--primary-text)]2/21 Central Park Drive, Yandina, QLD, Australia, Queensland[/COLOR]
[COLOR=var(--primary-text)](07) 5319 1234 Cheers COL[/COLOR]
Brettoh, re your initial post, "I can rev to 5900 now and can trim to hit the rev limiter". this stuck out to me. With the smaller block sizes i'd be looking to hit the rev limier at "light side day trip load" but at regular operating trim. I recon we can all get them all to hit the rev limiter with trim! Although on a mono i went through 3 sets on twin zuke 140's. Ended up with large diamater 3 blades, tried 4's and other 3's. Unsure about the zuke 70's but the 140's are very toppy and once i found props with good blade area but could get 6200 at neautral trim on flat water the whole shebang was/is running tops. Just my thoughts anyway.
Scott
cheers,Solas up the sunshine coast will cup your prop some more & it can make a grate difrance to the performanc
- [COLOR=var(--primary-text)]2/21 Central Park Drive, Yandina, QLD, Australia, Queensland[/COLOR]
[COLOR=var(--primary-text)](07) 5319 1234 Cheers COL[/COLOR]
I am speaking with Solas about thie Prop solution
The genuine suzuki props have lots of cup and grip. The stainless genuine are a bit better than the alloy ones. After mucking around with 5 boats with suzukis and countless genuine and after market props I always find the best performance with genuine stainless steel props. I believe this is because of Suzuki's higher gear ratios than other brands. The genuine props are designed for this slower rotation.
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