offshoreratboy

This one is for the prop guys... I have an 88 Formula 357 with 420's and TRS drives. Drives are not deep. 1.5 gear with Mirage 23s spinning outward. I can only get it up to 53 MPH on GPS @ 5000 rpms. I tried a set of Hydromotive 4 blade 25s and could only get up to 4000 rpm and 50 MPH. Any prop sugestions?

Poorsche

I'm interested in feedback you get on this--I've an 87 SR357 with TRS drives and 21P props/1.5:1 drives that I think are deeper in water than previous drives. I'm only gettinhg 4000RPM at WOT as well. Speed is around low 50's with 3/4 fuel and water.

I'm goin g to measure the X dim in next day or so and get the prop part numbers so we can compare results.

I've got MarinePower EFI 454's tht the manula says should max at 4800 RPMs. The old carb'd Merc 370's turned low 5000 RPM/s and WOT speed was in high 60's.

I have added a lot of stuff including Genset, lots of electronics but not more than 1000 pounds total additional load I don't think.

I'll update specs on next day or so. I'd like to get the engines turning in optimum performance range and if possible get a little more speed.

alter ego

I have a similar problem with my boat.... My thread is in here too. I have a shallow drive and I'm going to try a 4 blade prop so I can get a little more blade area. I think you might want to try 4 blades in a 23" or 24" pitch. That should give you more blade area so your slip numbers will be lower and still turn the rpm's so you are closer to your peak hp. I'm not an expert but your problem seems similar to mine and thats what I've been hearing from the guys on the thread. Good luck.

throttleup

It's helpful to know how much deeper the center of the prop shaft is in relation to the bottom of the hull. This gives us a good starting point. Excessive slip can be caused by a drive that is too deep or too high. Either one can cost you speed and handling.
When calculating slip with a regular Mirage we use 1" less pitch than what the prop is marked. With the Mirage plus use the marked pitch.
Your drives seem to be too high. I don't think a prop is going to get the slip to an acceptable level. The other issue, in your case, is with a non step bottom boat the drive needs to be deep enough to carry the bow.

Matt

offshoreratboy

Wow, that sounds like a whole bunch of work! I Built these engines and I would not want to go through the hassel of yanken em again! I believe you are correct about the drive hight because the stock gill trs riser just bareley touches the engine hatch. Which I would guess this means that the drives are high also. I will try to get the measurment on the prop shafts in relation to the hull bottom and go from there. If this were corrected with 500hp on both sides what do you believe I can achieve with this boat? I know its a heavy resin bucket but 50mph just blows!

Poorsche

Got some real data about my SR357's current config with rebuilt drives fro comparison--

Measurement from CL of engine shaft to CL of prop shaft is 26"---prop shaft is 9" below bottom of V--drives are spaced 33 1/2" apart and props are turning out.

Engines are only turning 4000 RPM's at WOT and top end per GPS is around 50.

Like I said I've made the thing a luxo-barge with all my electronics and chit but engines should spin at 48 at WOT per manual from MarinePower (454 EFI's).

My Next experiemnt is to try a pair of OLD TRS cleavers that were in the storage compartment on the boat when I bought it.

The mew drives look like they have a long low end compared ot revious units but I haven't checked that yet.

Comments?

lakepop

357 sr1 22" hydro motive"s four blade 3/4 fuel 2 people 64.3 mph gps 5000 rpm 23" mirage 63.8 mph 5000 rpm better handling with hydro"s easier to come on plain.

offshoreratboy

Yours is very close to mine with the 23 mirage's. I threw on my scuba suit and got under the boat and scrubbed anything I could find off of it, three hours later I was blue from holding my breath. It's amazing how much junk accumulates under where the bunks are situated when on the trailer. I cant beleive that that little bit of growth (4-6" stripes 12' long) would have such an effect. I had a full boat 4 adults and a full tank of fuel and I ran 60.8 on GPS @ 5000 rpm in glass top water. That is the fastest run since I've owned this tub. And it gives me hope! My hydro-4blades (24") would only turn 52MPH @ 4000 RPM. The only problem was the handling of the boat was terrible compaired to the 4blades. Julie from Throttle up says I should be able to get to 65MPH, with the right props of course. I will be calling her today...stay tuned.

Hydrocruiser

I was looking at a similar boat that was in my boatyard going for a low price. Similar engines and Hydromotove Turbo 3 blade cupped props...23P

Speed was in the same ballpark...low 50's on the spedo.

I called around and the solution is not cheap. The boat does not really plane as well as it should unless you have BIG power and it half sits back during cruise and never reaches it's potential.

The mechanic I spoke with said a combo of things are needed. First getting the HP to around T- 500-700. Then putting on extension boxes and trying out a few different props.

It's a big heavy boat that compares to some 39'er these days.
It just has a very low efficiency hull...it is a wave crusher and great in chop and more. It will go pretty fast in sloppy stuff and ride well...but to light it up that boat needs T-700 HP Zul's

Bottom line...it was too much work so I saluted and left.

offshoreratboy

Hey lakepop...What kind of power do you have. Mine are fresh 420's with some updates with the help of Dennis Moore. He designed the engines and I built them. He claims they will make 500hp. I'm not sure I'm there yet but they are more powerfull than the 420's were. I am still contemplating some carb changes, and I have a set of Vortech superchargers ready to go on this fall.