I want a 4 blade prop, but which one?

[cfauvel]

we are talking about a 1986 225hp Evinrude on 1986 21' Offshore Yachts (beefed up)

Ok went out today to get a WOT mark and here are some of my numbers using the GPS and Paddle wheel.

I estimated that the boat with 5 people and a dog and full live well, 35 gals of fuel weighs in at 3500 or so lbs.

No trim tabs are on the boat. The motor has a DoelFins= on the antiventilation plate, The boat runs and feels best with the engine trimmed in more than 0 degrees. Trimming out so that the bow lifts and rides the stern pad, does give me more speed, but starts to porpoise alot...just better keeping the bow down to cut through the waves.

I am running a 14.5 x 20" 3 blade raker.

I got the following numbers
RPM Paddle Wheel GPS SOG
3200 23 20
3500 27.33 22
3800 33 25
4000 37 28
4800 45 n/a
5100 50 41


I could not get the magical 5500 RPM, the closest was 5200. At 3500 RPM the boat falls of plane, 3800 RPM is about the slowest I can keep it on plane.

It takes about 7 to 10 seconds to get up on plane.

I want to be able to get up on plane faster, I want to be able to stay on plane at slower speeds and want to hit that magically 5500 rpm. I am not too concerned about top speed since WOT is not the ideal speed for gas and not easy to do in 2-4 foot sea.

I hope I have given all the info I can for people to help me pick out the right 4 blade. I've heard that 4 blades do exactly what I want.

Thanks

Chris

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

bump

 

[steelespike]

Re: I want a 4 blade prop, but which one?

Is the 5100 trimmed for maximum speed.You need to prop for that.
If you want quicker hole shot and stay on plane with less throttle.
A 4 blade prop is one solution.The Solas Amita has been a reliable selection.
Exact pitch would depend on your actual wot trimmed out speed and rpm.
The foil can help hole shot but likely hold down speed from drag.
Foil is usually a bandaid over a poor setup.

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

Is the 5100 trimmed for maximum speed.You need to prop for that.
If you want quicker hole shot and stay on plane with less throttle.
A 4 blade prop is one solution.The Solas Amita has been a reliable selection.
Exact pitch would depend on your actual wot trimmed out speed and rpm.
The foil can help hole shot but likely hold down speed from drag.
Foil is usually a bandaid over a poor setup.

With the motor trimmed out I get no better than 5200 and it porposies too much.

On my next outing I'll remove the DoelFins to see what numbers I get.

I was thinking of getting Smart-Tabs, but fitment is an issue with my engine bracket with integrated swim platform and ladders. The ladders are the issue, they deploy to the sides, parallel to the transom, rather than straight out the back. The tabs are supposed to be placed at the farthest location before the chines, well that would interfere with the ladders, so the tabs would have to come in torwards the center line about 10 inches maybe less.

Not sure if you can see the ladders inthe attachment, I'd move the transducer and paddle wheel towards the center line more if I had to.

 

[steelespike]

Re: I want a 4 blade prop, but which one?

Tabs can really help hole shot and control porpoising,smooth ride,reduce no wake speed wander.
They do however slightly reduce speed and mpg.
The 4 blade prop could reduce porpoising, slightly improve ride.Improve low to mid range performance.and improve handling at the dock.

 

[mpsyamaha]

Re: I want a 4 blade prop, but which one?

i have the same boat... mine is a 1987 hull with a 98 200 evinrude ocean pro, no bracket on mine though. i use a 3 blade 17p powertech prop and it turns 5600 at 45 mph on GPS with a lightish load. even with six people on the boat and a full tank it runs low 40s at WOT. i dont have trim tabs, and dont feel that its necessary. the holeshot is very fast on this boat, which makes me think you just have too much pitch on yours. since you have the bracket a 4 blade might be good for stern lift, but i bet having the right 3 blade would wake that boat up.

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

i have the same boat... mine is a 1987 hull with a 98 200 evinrude ocean pro, no bracket on mine though. i use a 3 blade 17p powertech prop and it turns 5600 at 45 mph on GPS with a lightish load. even with six people on the boat and a full tank it runs low 40s at WOT. i dont have trim tabs, and dont feel that its necessary. the holeshot is very fast on this boat, which makes me think you just have too much pitch on yours. since you have the bracket a 4 blade might be good for stern lift, but i bet having the right 3 blade would wake that boat up.

No freaking way!!?? not too many people have this hull or know the manufacturer. Do you know how hard it is to find specifics on this hull with the brand name like offshore?

I love the looks and ride, but man the workmanship was horrible, did you have to do anything to yours?

Mine got new transom, stringers, floor, tanks, engine bracket, and thickened hull in 1995. In 1992 when I bought it the transom and floor were soft (probably the stringers too, so we are talking 6 years , I understand they didn't encapsulate the wood for the floor/deck so it was bare wood on the underside.

My "new" boat is much more solid and strong (from water line down, still have the thin sides) and sits about 1 " deeper than the old water line,

Yeah I think i'm over pitched too, what is your minimum planing speed and time to plane?

Send some pictures!!

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

Tabs can really help hole shot and control porpoising,smooth ride,reduce no wake speed wander.
They do however slightly reduce speed and mpg.
The 4 blade prop could reduce porpoising, slightly improve ride.Improve low to mid range performance.and improve handling at the dock.

What causes porpoising? Is the prop lifting the bow then the weight of the bow is too much and falls down to where the prop can lift it again? or something else?

 

[steelespike]

Re: I want a 4 blade prop, but which one?

A rebuilt hull could be the culprit.Its possible a little rocker was introduced into the bottom.
A string stretched along the bottom might show up any bulges or rocker.
The 4 blade prop usually improves stern lift and reduce bow lift.
Some boats have a little rocker to help get the boat out of the water.
The 4 blade may allow you to raise the motor on the transom.

 

[mpsyamaha]

Re: I want a 4 blade prop, but which one?

Sadly, yes i have had to work on my offshore hull as well. It had a new floor put in it by the previous owner, which looked nice when i bought the boat a couple years ago, but i eventually found out that it was done real half assed. A while back one of the gas tanks started leaking... when we cut into the floor we found that the floor was rotten. then after more cutting found out the stringers and transom also had started to rot. So the boat is currently gutted to the bare hull. i already have most of the supplies to put it back together, but the hot wet summer has me and my friend wanting to wait for next fall to finish the project. This hull is just too sweet to let it go to waste. not to mention its going to be a sweet custom boat when finished.

found a couple pics on my computer... i have some more on my phone of the hull as we were gutting it out. i can upload if you want to see.

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

A rebuilt hull could be the culprit.Its possible a little rocker was introduced into the bottom.
A string stretched along the bottom might show up any bulges or rocker.
The 4 blade prop usually improves stern lift and reduce bow lift.
Some boats have a little rocker to help get the boat out of the water.
The 4 blade may allow you to raise the motor on the transom.

Not sure what a rocker is, but the hull thickening was done on the inside, unfortunately the gel coat is original.

I am pretty sure we introduced alot more weight to the boat with the rebuilt transom, thickened hull and engine bracket.

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

Yours is a lot cleaner looking than mine. Mine doesn't shine at all

Yeah post more pictures, maybe start a thread on the repairs.

Where are your batteries, mine our under that cubbard in the transom, room for two batteries, oil tank, battery jumper and what's left is about the size of two batteries.

The hatch on the starboard side stern is for the fuel filter/water separator, bilge hoses and fuel hoses, the hatch on the port side stern is weird. Super tall with thru-hull plug at the water line, shaped like a rectangle so not well suited for a live well, ends up being my storage area.

My leaning post has a big storage area and spots for 4 rods, but the angle of rods make it so you can't walk behind them....

just stern of the leaning post is my bait well that there from day one, but never plumbed until last year....hated drillign a big a s s hole thru my pristeen transom, but I made sure I sealed the hole before inserting my bronze thru hull and more 5200 was placed under the mushroom and more 5200 was placed inside the bilge area when I screwed on the seacock.

At the casting deck, there is a hatch that opens up to a very large storage area, I once had 8 scuba tanks there. The floor rotted, so the floor has been repaired and currently has a removable patch between the two middle stringers just for more storage as well as another hatch. Debating as to whether to make the patch permanent or leave the it removable. The small hatch is about 1' x 2' .

 

[earringboy]

Re: I want a 4 blade prop, but which one?

I didn't like the Solas Amita 4 on my 1979 Sylvan 18 ft deep V aluminium with a 1986 Merc 115. Steering effort was greatly increased and the bow seemed to be pushed down making me get thrown about by waves easily. I got 38 mph (gps) @5500 rpm. I put a Quicksilver Black Diamond on and it was much much better. Steering effort was reduced drastically ( push pull cable) I hit 41.4 mph @ 5500 rpm. Boat rode much much better, I was about 150 lbs lighter with the 3 blade. I'm inland if it makes a difference.

 

[cfauvel]

Re: I want a 4 blade prop, but which one?

I was looking at your photos, while in the water...My real water line is at the top of your painted water line, up until about half way towards the middle (around the rod holder closest to the bow), from then on the real water line follows the chine. I am sitting way deeper than you , probably because of the extra weight from, more fiberlgass resin, and engine bracket and beefed up transom. The propgods.com suggested I look at the anti-ventilation plate while running to see if I should raise the engine a few holes.

 

[mpsyamaha]

Re: I want a 4 blade prop, but which one?

ill try to dig up some more pictures for you. give me a day or two. i definitely have more of the boat in the water and as we were dismantling it.

i have only seen one other of these hulls in person before. it has been restored pretty well and the entire thing is lime green. if i see it and can get up close to it i want to take a picture, its crazy looking.

 

[cfauvel]

well after a litany of issues, ranging from cracked fuel distribution manifold (a little plastic thing at the base that supplies gas to all six carbs), various air leaks and lastly loose magnets.....with the old raker I got 5500-5600 rpms at 45 MPH....

then went shopping for the 4 blade ...went with an Power Tech OFS4 16"P...got better holeshot, and no cavitation and WOT of 5400 RPM @42mph.

then tested a Quicksilver Q3 17"P....slighter better holeshot still, no cavitiation and WOT of 5800 rpm at @47.6 MPH....

settled for the Q3