Am I under propped?

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bjanakos
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Am I under propped?

Post by bjanakos » Tue Nov 14, 2017 9:55 am

I bought by 1978 F-32 when I was fishing up north in Lake Michigan. The main fishing tactic there is slow-trolling for fresh water Salmon and Trout. Trolling speeds of 1.5 - 2.8 kts are common. We also didn't have to travel very far.

Now I am in the Gulf and wanting to fish costal and off-shore. For some reason, the boat just seems sloooooow in the salt water even though it's sitting about 3" higher. With that being said, I am getting about 10-12 kts at 2800 - 3000 rpms with origional Chrysler 360's. This is with a clean bottom and running gear and I really have no problem getting on plane at 2800 rpms. I get another knot or two when I trim the boat a little.

Are these expected performance numbers? I'm starting to think the previous owner put on slower props to get the trolling speeds down. I don't need to troll that slow any more. I don't know what's on there right now, but I'm going to haul out for maintenance soon and I would like to know what should be on there....

Thanks in advance.

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prowlersfish
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Re: Am I under propped?

Post by prowlersfish » Tue Nov 14, 2017 1:00 pm

Could be some growth on the bottom , What is your wide open rpm ? Gear ratio ( F32s used 2 different ratios )? prop size now ? I have some of the prop numbers but need the ratio .
TROJAN F36 Conv.
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captainmaniac
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Re: Am I under propped?

Post by captainmaniac » Tue Nov 14, 2017 1:34 pm

I believe props should be 3 blade 16x16 cupped. You should be getting better speeds than that. At dead slow idle (both engines) I do about 3-4 knots - maybe a touch more - depending on wind direction and strength. On a single engine I am still doing at least 2-3 knots.

I am running 360's as well on my '79 flybridge sedan. Cruise at 2800-3000 should be in the 16-20 range or maybe a bit more since you don't have the extra weight of the flybridge. You should be just barely on plane (with tabs full down) around 2200 RPM and doing about 12 knots.

Here is a speed curve based on averages of speeds observed at various RPMs over 17 (wow) years. One of these days maybe I will add markers for high and low speed seen for each RPM... Speeds are in knots as reported by my GPS.

The 'sweet spot' for displacement cruise is about 1500 RPM (8 knots or so), and fast cruise is around 3000-3200 RPM range - just before the secondary barrels open on the carbs and start guzzling that much more fuel for little speed gain.
Speed Chart for posting on forum.JPG
Speed Chart for posting on forum.JPG (89.42 KiB) Viewed 785 times

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bjanakos
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Re: Am I under propped?

Post by bjanakos » Tue Nov 14, 2017 5:31 pm

Thank you.

Both engines in at 600 RPM idle speed, I'm around the 4 kts range, but wit one motor in gear, I can easily do 2kts or less in dead calm conditions. But I'm not even coming close to those kinds of numbers on the top end.

I'll save this for haul out and check those props.

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Re: Am I under propped?

Post by prowlersfish » Tue Nov 14, 2017 5:53 pm

If you have a reduction of 1.5 to 1 it calls for 16x16 if you have a 1 to 1then its 14x 10 Normaly the 360 came with 1.5 to 1 . 318 were a mix and I have seen a few 318 repowerd with 360s that stayed with the 1 to 1 . That's why I asked about the ratio ( and WOT RPM )
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
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captainmaniac
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Re: Am I under propped?

Post by captainmaniac » Tue Nov 14, 2017 6:13 pm

bjanakos wrote:Thank you.

Both engines in at 600 RPM idle speed, I'm around the 4 kts range, but wit one motor in gear, I can easily do 2kts or less in dead calm conditions. But I'm not even coming close to those kinds of numbers on the top end.

I'll save this for haul out and check those props.
Silly question... are you measuring speed with GPS or onboard speedo?

At the 2800-3000 rpm (10-12knots) speed does your wake look something like this (shot from the fly bridge)
IMG_1071.JPG
IMG_1071.JPG (207.92 KiB) Viewed 773 times
Or is there a much bigger 'hump' right behind the boat (as in less than 10' away) and several obvious visible 'rollers' following that (can't quickly find a good picture of this scenario)? If it looks like the pic I attached, you are probably going 18+. If it is the 'near hump with rollers', and any slower you have water flowing back to the transom, then you are just barely on plane, and yes probably in the 10-12 range.

You are probably using a GPS, but had to ask... on board speedos can be notoriously inaccurate for so many reasons.

If you are getting 'normal' speeds at idle you should get them at higher RPMs too, unless the boat is fouled, props are fouled or badly misshapen (so cavitating at speed), or the boat is super heavy or waterlogged.

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Re: Am I under propped?

Post by prowlersfish » Wed Nov 15, 2017 12:54 pm

Your had this same issue a few years back . Have you been dealing with it this long or has it just came back ?
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
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bjanakos
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Re: Am I under propped?

Post by bjanakos » Wed Nov 15, 2017 7:13 pm

captainmaniac wrote: Silly question... are you measuring speed with GPS or onboard speedo?
Well, I usually just wet my thumb and stick it out the window. :mrgreen:
captainmaniac wrote: At the 2800-3000 rpm (10-12knots) speed does your wake look something like this (shot from the fly bridge)...
Or is there a much bigger 'hump' right behind the boat (as in less than 10' away) and several obvious visible 'rollers' following that (can't quickly find a good picture of this scenario)?

If you are getting 'normal' speeds at idle you should get them at higher RPMs too, unless the boat is fouled, props are fouled or badly misshapen (so cavitating at speed), or the boat is super heavy or waterlogged.
I am getting a much more pronounced rolling wake in the back than you have. The wake rolls outboard and are much taller than yours. They break over like a surfers tube.

And yes, I have a hump following 6 or 8 feet off the transom, and yes, I am getting my speed from the SIMRAD evo2. I have a diver service come out every 3 months to de-foul the bottom and running gear. The only thing that he has no listed as "Excellent" conditions the shafts, which he rates at "Good". Bottom paint was done 16 months ago and the diver was here less than 2 weeks. So I'm going on record that the bottom check out as stated in my first post.

One thing yet to consider are the tachometers. One of them is definitely off and reads higher than the other (I flipped them). There is a possibility I'm not actually running at the RPMs I think I am. But I have a pretty good ear and I think the good one is in the ball park because I hear the secondaries kick in at around 3200.

As far as being water logged, and over burdened with weight. As stated in my first post, the boat sits about 3" higher in the salt. My exhaust was sitting just above water level in fresh water. Now they are 2-3 inches above water level. If I had to guess, I would say I have about 12" - 14" of draft on the center line aft.

I currently have this boat up for sale, but if I can fi this speed issue with a simple change of props..... This might be a game changer.

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Re: Am I under propped?

Post by mikeandanne » Wed Nov 15, 2017 9:14 pm

Don't know if possible but could your diver just read the numbers off the props, that might tell the story for sure.I had 360's and was under propped at 14 pitch, repitched to 16x16 and all was well.
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Re: Am I under propped?

Post by bjanakos » Thu Nov 16, 2017 9:06 am

mikeandanne wrote:Don't know if possible but could your diver just read the numbers off the props, that might tell the story for sure.I had 360's and was under propped at 14 pitch, repitched to 16x16 and all was well.
I already have a note out to him on that and also asked for a quote to swap them on his next visit if that is indeed the case. However, to do plan to haul out after the holidays to address the stuffing boxes and wax the hull. So I may skip the next dive.

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Re: Am I under propped?

Post by bjanakos » Sun Nov 26, 2017 7:04 am

mikeandanne wrote:Don't know if possible but could your diver just read the numbers off the props, that might tell the story for sure.I had 360's and was under propped at 14 pitch, repitched to 16x16 and all was well.
I'm curious, were your symptoms similar to mine? The diver said he would do his best, but it's a difficult task.

I have a new strategy... I'm going to get with the dry-stack guys at my next fuel-up and offer them a nice tip to just lift me out real quick and see if we can get a reading.

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Re: Am I under propped?

Post by prowlersfish » Sun Nov 26, 2017 7:48 am

You should pull the props and have them checked at a good prop shop . There could be unseen damage and be off pitch from what they are stamped ( seen it a lot). And get the tachs right so you know what your rpm really is .
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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Re: Am I under propped?

Post by bjanakos » Sun Nov 26, 2017 8:59 pm

Went out today for a run. I brought my fathers SnapOn tachometer tool and validated the starboard tach is pretty much dead-nuts-on.

Here I am at 700 RPM - Both engines engaged - Barley 3 knots. Its usually somewhere just under 3. We were right at a low slack tide and winds were light an variable. Recent dive job, so fouling should be negligible.

Image

Image


Once I cleared the no wake zone, I brought here up to 2800 and barley 10 knots.
Image

Image

And here is a pic of my wake....
Image


Not much of an improvement over 2400 RPM
Image

Image


My starboard stuffing box is getting leaker than I like and my transducer bracket has come loose. So I may as well go all in on a proper haul out.
Last edited by bjanakos on Fri Dec 01, 2017 9:06 pm, edited 13 times in total.

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prowlersfish
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Re: Am I under propped?

Post by prowlersfish » Sun Nov 26, 2017 10:02 pm

I can't see the photos ( could be a issue on my end)
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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captainmaniac
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Re: Am I under propped?

Post by captainmaniac » Sun Nov 26, 2017 10:25 pm

Paul - think it is an issue with the post itself, or Bjanakos may have posted the pictures in in a way that they are password protected or not publicly shared, or they may be shared publicly but he has shared 'private' links. I can't see them either.

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