Thoughts on prop load for com-fish/tow boat

[NWestward]

First, my assumptions:
A. Boat is over-propped if it cannot reach rated RPM at WOT
B. Boat is under-propped if it bests 105% rated RPM at WOT
C. Towing a seine is basically pushing throttle against a brick wall/towing a massive sea-anchor against the current

Second, where I’m coming from:
A. Commercial fishing with a displacement vessel (seiner).
B. Vessel is 55’ x 15’ and weighs ~76k lbs without net or product load. Fishhold capacity ~80k lbs.
C. Main rated to 325hp, with 28x28 4-blade prop. Prop has 2.5” clearance from hull and 1.75” from keel shoe/skeg
D. Vessel operates ~70% with the main-hold full of water (regardless of fish), carrying a 12k lb net, and pulling a 9k lb jet skiff. (Of that time, ~30% is cruising & ~70% is towing net at low/variable/up-to-max RPMs)
E. The remaining ~30%, the vessel is cruising continuously, unloaded of the above.
F. Vessel hits about 200 under rated RPM at WOT, unloaded. Regular cruise speed is <10knts (<1800 RPM).

Obviously a boat that tows (& increases its mass/loads so significantly at times), must strike a balance with HP, transmission-ratio, & prop.

Third, my questions:
A. Would you be worried about my not reaching rated RPM?
B. If so, should I prop the boat for unloaded or maximum loaded (towing net) conditions? Or how to find a balance in between?
C. By some general rules of clearance, my prop *should* be smaller diameter. But is that an issue if I don’t have noticeable vibration or noise?
D. Would a different style prop (4-blade, 5-blade, or fixed nozzle) be able to increase: WOT RPMs, fuel efficiency, cruising speed, &/or bollard pull with my existing engine/transmission?
E. The downsides of the above prop options?

As this is an electronic engine (JD6090AFM), I could increase rated HP, but don’t know if that would change anything for the RPMs I generally operate at?

In a dream world, I would put in a larger displacement engine and run a much larger diameter prop. But a repower and transom redesign are likely just pipe-dreams for the foreseeable future. (Heck, might as well make it a 58’x20’ while I’m at it)

 

[baeckmo]

What's the gear ratio?

 

[NWestward]

3:1

 

[comfisherman]

Curious what hull you have.

This is the light/loaded conundrum facing all seiners. Overwhelming percentage of our boats were built before our holds were rsw. Even more were built with larger hp engines during the high price of herring an salmon, being re powered int he late 90s and early 2000s when the market crashed similar to what it's doing now. The end result is a boat with way less power and significantly more weight than the hull design factored in during the 80s when the boat was likely designed. Add to that we all want to fish in 30 inches of water all the while packing a much weight as we can.

Right out front, there is likely no perfect answer. 55 feet and a 28 inch wheel with a tank full of water that weighs 75k pounds doesn't have a "best" case scenario, just "least worst". All tweaks we do will be minimal, and you're going to have to do the cost analysis on if it's worth it for you or not. Most props end up on these boats for several reasons. A. it was on from the last engine, B. my buddy had one in his gear locker when my correct prop hit a rock and it's never been swapped out, C. We slightly overloaded it as we never used the upper rpm and this got a decent engine load... could go on for a while but you get the gist. Your likely putting more thought into a prop selection than 95% of the guys your fishing next to Ill try and respond to the questions.

Third, my questions:
A. Would you be worried about my not reaching rated RPM?
This is a 6090 and should have engine loading, keep an eye out on that when your setting and cruising to see if your overloading the engine.

B. If so, should I prop the boat for unloaded or maximum loaded (towing net) conditions? Or how to find a balance in between?
Personal preference, my last boats had different props. One for the part of the year and one for when the pinks showed up and we'd spend 2 months heavy and slow. In my case my heavy slow prop was also a battle axe that had already made bottom contact. My current setup is a veem for spring and fall and a stainless Michigan workhorse for chasing fish in shallow. About 4 inches of pitch difference on the current setup, that's just how the math worked light/loaded. More than just a few boats pick somewhere in the middle and let it ride, probably how your boat was setup.

C. By some general rules of clearance, my prop *should* be smaller diameter. But is that an issue if I don’t have noticeable vibration or noise?
If no noise, or obvious cavitation issues I'd let it ride. Most these tunnel hull seiners fly in opposition to all the rules of thumb, if it works stick with the larger wheel.

D. Would a different style prop (4-blade, 5-blade, or fixed nozzle) be able to increase: WOT RPMs, fuel efficiency, cruising speed, &/or bollard pull with my existing engine/transmission?
Minimally for all of the above. 4 blade is the norm, 5 blade usually adopted by guys who tried cramming to much power in a small wheel or a wheel to large and are trying to mitigate noise or cavitation. Fixed nozzle would make an even smaller wheel inside the nozzle not sure with all the seine tunnels I've seen it would be a beneficial retrofit. 325 hp would be hard to put in a nozzle 28 inches in diamter, then you have the difficulty of steering.

E. The downsides of the above prop options?

I think you have slight engine loading room for improvement, but most the options are likely going to minimally change speed and performance. Engine re flash doesn't meaningfully change torque curve on a boat that heavy, high skew 4 or 5 blade might pick up a couple tenths but that has to be weighed against cost. Nozzle is cost plus some serious surgery and probably an articulating rudder to not feel like a train on a track...

4 blade 28 inch wheel is 2800-4500 dollars, pick a pitch to your most common weight and rpm. Re pitch an existing prop is a couple hundred, might be the best place to start.

 

[NWestward]

1988 50’ Ledford. In 2012 it got a 5’ stern stretch and the John Deere/transmission. Also, an articulating rudder (Thank goodness, it’s pretty maneuverable. Without, I think it would already be like a train).

Last summer was my first as its owner. So far I just do summer season, splitting my time between tendering in the Bay and seining. So I’m in the “best-worst” one Prop to rule them all category.

With your seasonal swap, I assume the Veem has more pitch than the Michigan? For when you’re lighter vs heavy?

I’m thinking this might be my “forever boat.” So trying to get the most out of it. Improving & preserving its systems as I can.

I will look for my notes from last summer, to see where I limited out on RPMs while towing seine.

 

[NWestward]

I have to admit, the idea of a nozzle peaked my interest. The idea of more bollard-pull with less engine load sounds like a unicorn… something to research and daydream about, at least.

I don’t know of any boats my size that have tried one?

This boat is like a semi-truck. Heavy and slow and draws quite a bit when tanked (a PWS jet seiner or fast herring boat I am not).

 

[comfisherman]

Hard chine millenium hull?

Keep in mind you gain some thrust with the nozzle but would also loose with much smaller diameter prop. A 28 inch nozzle for our speeds is probably smaller than needed for that level of horsepower. Can only think of one that tried it in southeast and it eventually went back to an open wheel. Even the 58 class deep draft boats are trending towards open props from nozzles in the early 2000s, the thrust isn't worth the squeeze for our work. Skiffs designed around it and just doing raw static pull are about all the best use of nozzles in seining.

Yes the veem for long lining and traveling to and from with more pitch.

I wish our shallow draft tunnel hull seiners were semi trucks.... mine is a toyota tacoma pulling a full 53 foot van.

 

[NWestward]

Ha! My last boat was like a Toyota hilux. Not fast, nor strong tow, but light & could maneuver like a car. If not a semi-truck, then this Ledford is like my 98 dodge diesel. Heavier to start & stop, & doesn’t pull as much as one think it would?

Not sure what you mean by “hard chine millenium hull.”

Pretty flat-bottomed (good for the Bay, even if I draw more than I used to), with rounded edges. With the stretch he also added decent sized rolling-chaulks. I wish I knew more about the pedigree of Ledfords… I’ve always liked them aesthetically. I know that after mine they made some twin screwed and a couple that are 1-2’ wider and swing a 38” prop (with more clearance above and below than I have). *Drool*

Alas, digging around the W/H today, I couldn’t find any notes of my towing RPM/load. I’ll try to take better notes this summer.

If only as a thought experiment, I think I’m going to make an inquiry with the nozzle salesmen. I was talking with a local boat builder about it today. He said the last 12L he installed was over $100k, before transmission and labor.

 

[NWestward]

… Not because I think I’m smarter than anyone else. But, I am curious to hear what they sell & if it would help. And if it *could* offer benefits, I bet it would be cheaper than $100k

Like you said about props on our boats. Most everyone up here does what they do because:
A. Their buddy did it
B. They got it cheap/free
C. They talked to a local who had done it before on another boat, and that person liked how it worked out (no follow-up necessary).

Honestly, I’m the same way. With a buddy I cut my old boat in half and added 6’ (with the blessing of the local guru) & it worked as good or better as we’d dreamed.

And, it is a thing I love about this niche world.. I call my long walks “yard/harbor surveys.” Just daydreaming.

 

[comfisherman]

Cnf in Mississippi does nozzles. He's significantly less cost than west coast makers. In the last couple years he's done some for a southeast landing craft with flat tops for tunnels. Allowed a slightly bigger nozzle, guessing some performance degradation but all this is a balance. He's like 7-10 grand vs the Ballard outfits 26k...

Yeah a scania is about 80k, a John deere is 77. Add hydraulics and a bigger gear, plus a larger cooler and some exhaust work and 100k is probably on the low end. Not a crazy amount considering the cost of things, but in terms of pinks and reds at the prices were gonna have the next few year...... yikes.

My money, I'd buy or borrow David Gerrs propeller handbook, sit down and play with the numbers on light vs loaded and buy a good 4 blade prop. I'm liking the teiginbridge and veem style these days. Seem to work pretty good in the shallow tunnels. That said if your grinding in the shallows chasing humpies or set net contracts in the bay I'd probably stick with a workhorse style. Just hurts less when you roll a fluke. Probably size it cheating the loaded side, just be mindful of overspeed light.

 

[NWestward]

Thanks for all your responses and tips. The internet is a great resource for a lot of boat systems. But forums often skew towards planing hulls or sailboats. I’ve often wondered what I would glean from seeing what people are doing with our size of commercial displacement boats in other places. Eg. Eastern Canada, Iceland, Northern Europe.

And agreed about the fish markets. Between fish prices, insurance cost, and interest rates… most of my summer paycheck is earmarked for paying debt/overhead, and there are other systems on the boat that more urgently need investment…

Maybe I’m feeling the spring day optimism, but I’m cautiously optimistic that this summer will sort of be a “reset” on price degradation (with decreased salmon runs forecasted across the state). Banner year 2025?

 

[NWestward]

For my research, what is the outfit in Ballard that does nozzles?

 

[comfisherman]

I wish I shared your optimism for the market, but having lived through the crash of the late 90s as well as the 15/16' one this is much more like the one in the late 90s. The emerging markets that pulled us out from that slump are persona non grata to our ruling class. Might be a while for us to find viable replacements.

Ballard brass and propeller made the casting for the steerable and fixed nozzle on most the mavrik/rozema type nozzle skiff. Can't for the life of me remember whose doing the casting and machining now. Have it in my desk as from a quote last fall, I'll try and remember next week when home. It was 26k roughly for a 28, cnf was 6700-9k depending on amount of stainless and adapters pre welded.

Didn't call Rice, but back when we were looking for the big boat they were somewhere in the middle of nautican and cnf.

Lots of cool stuff internationally but not much of the hull design transfers over. Not a ton of other places trying to seine in shallow water, were sorta unique in that. Add to it only the bay has been profitable enough to push innovation in the last few decades. The few new boats are essentially chubby versions of what 1991 had to offer, don't get me wrong I'd love a big new 58 out of the new moe mold. But it's fundamentally just a chubby 52 beck designed in 1990.

Just rolled under a big boy Ledford, didn't realize some had such small egg beaters. My limited big Ledford experience was on a deepr variant with a 30 some odd inch wheel. Not a ton of room up under there. Was the stretch mid body or stern?

 

[DogCavalry]

ZF makes 2 speed marine transmissions, for vessels that have a marked difference between heavy and light conditions.

 

[NWestward]

The stretch was on the stern. Which makes laz rather reasonable for fuel tanks and generator. Deck space for net & needed flotation. Didn’t extend shaft/steering gear. Of course, I wish he’d stretched in the middle, and changed fish-hold bulkheads around. Has a significant beam taper & hull rise in the stern.

I’ll have to ask around, but I *believe* only two Ledfords were made wider and deeper than mine (Equinox & Renaissance). Didn’t even realize they had made a twin screw. But saw one up for sale last year.