F-26 top end Q

[KWITCHYERBELEACHIN]

Hello all. I recently repowered my F-26 with a 260 mercruiser (chevy 350) In the process I added the Holley marine pro-jection. I am very impressed thus far with the engines manners (super smooth idle and fantastic hole shot for a semi-planing hull). However, I am only able to pull around 3400RPM WOT with a top speed of a around 18knt. She will cruise all day at 3000RPM and 15knts. and be smooth as silk. A little background before any answers. I had the boat hauled and the hull stripped, smoothed of some damage and slight blistering, all through hulls replaced with SS above water line and bronze below. New SS prop shaft, brass 14 x 10 prop, and new SS oversized rudder. Had the bottom antifoul coated with Pettit Hydrocoat for trailered boats, it is self polishing and has a reasonably smooth finish right now. Am I correct in trying to troubleshoot the fuel injection, or is there something else I should look into. I had a friend tell me he suspected my prop shaft was misaligned, says that will kill top end. Thanks for any help.

[k9th]

I would think if the prop shaft was misaligned you would feel a good vibration from the misalignment.

The fuel injection is a good place to look for the problem from the way you describe it. I would check the prop pitch and the gear ratio in the transmission to make sure they are correct also.

Just my 2c.

[MattSC]

I agree with K9th. If your prop shaft was out of alignment you'd have some sort of vibration. The fact that you can run 3000 rpm and it's smooth as silk, I think that your alignment is fine. As far as your prop, the 14x10 is correct for the boat. Did your fuel injection kit come with any software? I have a fuel injected Crusader, (chevy 350) and I'm able to connect it to my laptop and see what the engine is doing while its running. Sounds like there might be some sort of rev limiter. The other thing is check your fuel supply line/pump to make sure that it is capable of the proper fuel flow rate. I had to change my fuel water separator when I repowered as the original wouldn't pass enough fuel to supply the engine at WOT.
Your oversize rudder might add some drag as well, but I don't think it should cause that much of an rpm loss. Here's a photo of mine, which is a stock setup.

[prowlersfish]

What CFM did you get to replace your carb ?

[KWITCHYERBELEACHIN]

Thank you for the responses. I will try to touch on all of them. The fuel injection is Holley's 2B marine rated at a whopping 800cfm. It is the smaller of the two systems. 800 seems like a lot but again there wasn't a smaller option. My system does not have a computer uplink, I think you have to have the upgraded Holley Comander system. Mine runs closed loop and supposedly adjust fuel based on temp and RPM. I can adjust fuel mapping via onboard control knobs on the ECU. My rudder looks nothing at all like the one shown in the pic. I had a oversized balanced rudder installed. It is deeper on the front and rear of the shaft and does not have that "cavitation plate". It has made running at speed a bit of a learning experience as it reacts more aggressivly and tailing currents are more noticeable,especially in the "no wake" zones in our harbor requireing a lot of driver input. Straight ahead she is wonderfull, and I have considerably better dockside manners than before. I use a Racor water seperating filter and have it plumbed in such a way that it is also the manifold for the return fuel (fuel just makes a loop back into the second filter inlet) I honestly don't know the flow rating. Starvation would make sense though, I had to increase the WOT fuel map as much as it would go just to get it where I am now. But holey cow that's a BUNCH of fuel for a chevy 350. I am plumbed with 3/8 fuel lines everywhere, I would think there is more than enough fuel flow. Transmission is a velvet drive 1:1ratio. I have no idea how to tell if it is slipping, it doesn't get hot. And that thought crossed my mind as well, I am just not sure how to RPM the prop shaft to see if the tranny slips. Sorry such long post. But I just did a massive amount of work on this boat to try to give it a second life and just want to figure this out. Thanks.

[prowlersfish]

It your trans was slipping you would be getting higher rpm . Also if it was slipping its life would be very short , minutes if your lucky .

You may not like what I have to say but I will say it . your system seems like a miss match to your engine . EFI works great if its a factory system, but I have yet seen a add on system work right in a marine or street application .

[mccopps]

I replaced my 1977 F26 Chrysler 318 (225 HP) with a Chrysler 360 (260 HP). The transmission is still 1:1 however it changed from the Velvet Drive to a ZF-Hurth. In neutral the engine will rev to 5,000 RPMs however in forward gear the engine only gets to 4,000 RPMs.
My sea trail results are knots per hour with respect to the engine RPMs.

Prop---2.0k---2.5k---3.0k---3.5k---4.0k
13x9----7------10-----12-----13-----13
14x11---9------13-----16-----19-----20
14x9----8------14-----18-----20-----23

The 14x9 prop has slight cupping on the trailing blade edges.
The 23 knots is 26 MPH so I feel that I have the right setup now.

[Big D]

I trust your ignition system is up to spec; distributor, timing/advance etc? If not, doesn't matter what type of fuel delivery system you have, you will not reach WOT.

[gdsimmons]

I am with MCCOPS on this one. Your prop needs to be matched to your boat and engine combination. When the engine changes you will have to find the correct prop pitch to get max rpm.

Check out this link. It has a ton of info on choosing the right prop.

http://www.propfix.com/services_prop_education.php

[rossjo]

Any idea what the F26 weighs?

350 w/ FI should get about 300HP
1:1 Velvet Drives
14x10 prop
0% slip @ 3500RPM = 33mph = 28.8knots
So, you're getting 18knots = 37.5% prop slip, which is high.

You might need more diameter and 1-2" less pitch.
I see you have plenty of clearance for more dia, so 16x8 might work?

But, rather than guess, join BOATDIESEL - they have a great prop calculator. Otherwise, you'll get a lot of advice that you can't afford to try.

http://boatdiesel.com Prop Calculator _____________________________
Determine the correct diameter and pitch of a propeller for any given vessel and engine.
Define your:

• Vessel- displacement, semi-displacement or planing. Water line length in feet or metres and displacement in lbs, kgs, tons, tonnes or long tons
  Engine- output in SAE hp, kW or metric hp, maximum rpm, manufacturers rating of either pleasure, light, medium or heavy duty.
  Transmission- type and ratio.
  Propeller- number of blades and if need be define a fixed diameter.

The program will then calculate:Maximum achievable speed, estimated fuel consumption, recommended propeller diameter and pitch, a propeller pitch based on a required fixed diameter, plus it will suggest alternative propeller sizes using different gear ratios to provide better propeller efficiency.
If you define a cruising rpm, the program will calculate the power produced, estimated fuel consumption and cruising speed you can expect with this same propeller.

[mccopps]

The specs for the Trojan F26 are:
LOA = 26' 4"
Beam = 10'
Draft = 27"
Weight = 5,450 lbs
Fuel = 75 gal
Water = 20 gal

[MattSC]

I ran mine through the Boat Diesel Calculator several years back, according to the sheet, for my application F-26, 330HP 5200 max rpm results were:

Prop based on Input Diameter 14.0
Pitch 8.0
Blades 3 (cupped)
cruising speed 18.8kts @ 3100rpm @5gal/hr
Max speed 35.8kts
recommended a 12.1" x 10.4" cupped propeller
My boat weighed 7600pds according to the travel lift. Full fuel/gear

I ended up with a 14.0 x 10" 3 blade cupped propeller
cruising speed at 3100rpm, depending on current 17-19kts
Max speed @ 5100rpm 31.6kts gps ( against current)
fuel burn at cruise rpm 5.6 gal/hr according to laptop hooked to engine during test.
* according to John at Marine Tech the boat originally had a 14 x 10 cupped prop 225hp chrysler.

[rossjo]

PropCalc results:

3-Blade: