CONTINUOUSWAVE

PART ONE

I finally decided to re-power my 1990 Montauk 17. This boat came with a 1991 Mercury 90 HP (two-stroke) outboard motor when I bought it new in November 1990. The engine has served me well, and I have enjoyed maintaining it almost as much as running it. If I operated this boat primarily to pull kids around a lake on a water toy, I would keep it forever, but my use has evolved into intense 5-day fishing trips ranging over an isolated 1,000-square-mile coastal estuary with fishing partners who take a dim view of time lost to replace a relay or adjust a shift cable. Thus, despite this outboard motor working flawlessly at present, I am letting it go.

As I recall from the now-departed Whaler Central discussion board, the Montauk was the most commonly owned model among forum members, and re-powering a classic Montauk 17 is a popular topic on this and other forums, with over 900 matches on a continuousWave search for “Montauk re-power”. (For a recent discussion, including my rationale for choosing a Yamaha F70, see here.) However, I am not aware of anyone providing detailed performance data before and after the re-power of a Montauk 17 with a jack plate like the one on my boat, so perhaps this report will be of value to other owners considering something similar.

The first step was finding a dealer. Although there are more than 30 Yamaha dealers within 100 miles of where I live, hitting the “Repower Dealer” button on the Yamaha Outboards dealer search Web page narrowed it down to nine. After a few phone calls, I settled on one that had an F70LA in stock at a fair price, had a reasonable shop rate, and seemed willing to work with me on a few install details (although they did comment once that “Boston Whaler owners are a little different”).

Next, I removed the battery cables, wiring harness, and shift/throttle controls, and pulled off the motor.



Next step: choosing a propeller.

M

I hope more installments of this illustrated narrative will be forthcoming.

I am also interested in see more posts on the re-power of this MONTAUK 17.

PART TWO: CHOOSING A PROPELLER

I did a Google search recently for “Montauk F70 propeller continuouswave” and got 79 hits. Indeed, the question of which propeller to use for a Yamaha F70 on a Montauk 17 is so commonly posted on this discussion board that one of the moderators has a stock answer that he has used as a reply for several years. Here is his post from 2023:

Many owners have repowered their Montauk with an F70. (Wide open throttle is 6300). Their testing resulted in these recommendations:*

13 x 17 Yamaha Painted SS
13.25 x 14 Yamaha Performance Series
13-1/4” x 17” Turbo 1
13.25 x 14 PowerTech SCP

This answer is not consistent with what I found during my search. Among the 79 threads I reviewed, there were only seven that included objective propeller performance data, and these were all using propellers with pitches between 13 and 15-inches. The only propeller that had more than one positive review was the Yamaha Performance Series-3 13.25-inch x 14-pitch (part # MAR-GYT3B-V4-14).

I also found a test of the Yamaha Performance Series-3 13.25-inch x 14-pitch (part # MAR-GYT3B-V4-14) propeller on a Montauk 17 with a Yamaha F70 posted on YouTube (watch it here) that showed good performance (although the author found that a Powertech! RED-3 13.25-inch x 14-pitch propeller was a little faster at wide open throttle).

Two other propellers that I considered were the Powertech! SCD-3 13-inch x14-pitch (listed above as “SCP”), and the Yamaha Turbo Quest 13.125-inch x 15”-pitch (the lowest pitch available), which the manufacturer says is “very well suited for smaller utility/work boats and Yamaha F70 applications”.

There are pluses and minuses to each of these: The Yamaha props are ventilated, which can improve initial acceleration on heavy or underpowered boats, but the Performance Series prop is no longer being manufactured in this size. I couldn’t find any performance data with a Turbo Quest on a Montauk. The Powertech! props may be available on a trial basis (from Ken at Propgods.com or other sources).

In the end, I bought a new-in-box Yamaha Performance Series-3 13.25-inch x 14-pitch propeller from a marine supply store in Maine that listed three for sale on eBay. It’s a beautiful propeller, highly polished (although that isn’t supposed to affect performance), with one characteristic that I’ve never seen mentioned: it is quite light, at least when compared to my old propeller (See Figure 2).



Next installment will be "Sea trial."

M

Again, thanks for the very comprehensive information on the process of propeller selection for initial purchase --up to the point of the actual sea trials, whose outcome will be much anticipated.

Perhaps I am confused, but in PHIL T's remarks he mentions the "13.25 x 14 Yamaha Performance Series" propeller as a recommended choice. Isn't that the same as the "Yamaha Performance Series-3 13.25-inch x 14-pitch (part # MAR-GYT3B-V4-14)" propeller you decided to buy?

ASIDE ON YAMAHA PROPELLERS

The Yamaha-branded propellers are generally very good performers. As I recall, in c.2008 Yamaha propellers were actually being made for them by PRECISION PROPELLERS INDUSTRIES, and Yamaha decided to buy the company and bring propeller manufacturing into their realm of outboard engine manufacturing and sales. At the time Precision Propellers was marketing their own brands under the model designators or branding as STILETTO and TURBO. In c.2015 the STILETTO branding was dropped.

There is a rather good discussion about this in a thread in the old forum at

Yamaha Buys Stiletto Props
https://continuouswave.com/ubb/Forum4/HTML/006259.html

The "Precision Propellers" name lives on. Yamaha refers to their propeller division as "Yamaha Precision Propeller Industries." The manufacturing plant is still located in the Indianapolis, Indiana, area. The top page of their website explains the history of the company and how it came to be owned by Yamaha:

https://yamaha-indianapolis.com/#about

NOTE: one of the propellers in the recommended list from PHIL T was a TURBO brand propeller, which would very likely share the same heritage as the Yamaha propeller also in that listing.

Perhaps I am confused, but in PHIL T's remarks he mentions the "13.25 x 14 Yamaha Performance Series" propeller as a recommended choice. Isn't that the same as the "Yamaha Performance Series-3 13.25-inch x 14-pitch (part # MAR-GYT3B-V4-14)" propeller you decided to buy?

Jim, I am gratified that you have found my recent contributions of value, but I am sorry to see that they may have caused some confusion. My purpose in writing this narrative is in part to educate readers about this topic as you and others have educated me in previous postings, but it appears that my efforts leave something to be desired. Please allow me to make some clarifications.

You ask, “Isn't that the same as the "Yamaha Performance Series-3 13.25-inch x 14-pitch (part # MAR-GYT3B-V4-14)" propeller you decided to buy?” My answer is, “I don’t know, probably”. PHIL T did not specify the part number nor the number of blades on the prop; I have found Yamaha Performance Series props offered for sale with either three or four blades.

During my recent search of this discussion board, I found comments ranging from “Brand X props are lousy/great”, to “I tested a Brand X/Model Y prop (part # xxx) on this boat under these conditions and found this performance”. I think that the value of PHIL T’s post about propellers falls somewhere between these two extremes, and I included his comment (including the typographical error) as a gentle reminder to readers that they should approach recommendations about props with caution. I couldn’t find information on continuousWave about three of the four props he recommended, and the 17” pitch listed for two of them suggested to me that they might be inappropriate for use with a Yamaha F70 on a Montauk 17. If more performance information about those props is available, I would welcome it being posted on this thread, as I am aware there are readers who have far more knowledge of propellers than I.

Here is a summary of the propeller evaluations I found. There were actually 8 propellers evaluated rather than the 7 that I mentioned in my previous post. The dates are when the first post on the thread appeared:

2/27/2012: Yamaha Performance Series-3 14” pitch, 38 mph@6200 RPM WOT, 2 people and normal load. 16" pitch too much.

9/24/12: Stilleto Advantage 15" pitch WOT 5400 RPM, 13" WOT 6374 RPM rev limited.

7/19/2014: Yamaha Performance Series-3 14” pitch 3 holes up, 38 mph@6200 RPM (on 1999 Alert 17).

8/11/2015: Solas New Saturn 13.5" x 15" part #3431-135-15, 38 mph@6300 RPM WOT on jack plate with light load, 36 mpg with heavy load.

2/17/2017: Yamaha 14” pitch aluminum, 27mph@5200 RPM.

5/24/2019: Solas 13.5" x 15", 32.5 mph@5500 RPM WOT, 10 gal fuel, 400 lbs crew, 2 batteries.

I salute both PHIL T and you for your efforts and always look forward to reading your comments. Thank you for letting me be part of this community.

I enjoyed reading what you posted about Yamaha’s propeller manufacturing operations. After perusing the Precision Propeller web site, I have a much greater appreciation of the craftsmanship that goes into making a prop, and why two props that appear identical may be priced differently. Since we are digressing from this narrative, please allow me to share a personal story that involves propeller manufacturing. In the early 1980s, I purchased a coffee maker that was innovative for its time – the Toshiba My Café. It was a relatively simple machine that combined grinding with brewing, and it was very popular (it even made its way into Hollywood prop rooms, as I see it occasionally in 1980s movies like The Big Chill). When the heating coil burned out, I went to replace it, only to find that the machine had disappeared from the shelves. It turns out that the US Navy had noticed Soviet submarines had suddenly become 50% quieter in the 1980s due to improvements in propeller manufacturing using machine tools illegally provided by --- Toshiba. As punishment, Congress banned all Toshiba products from sale in the US, my beloved coffee maker among them.


(Yes, I am aware that submarine propellers are more properly referred to as "screws".)

M

Your most interesting sidebar on Toshiba is also much appreciated.

Regarding propellers for submarines, I have always pondered the notion that is often attributed to outboard engine propellers that ascribes to a particular propeller the capability to be bow-lifting or stern-lifting (or sometimes both simultaneously), and how that capability would be implemented (or avoided) on a submarine.

I will now get out of the way and wait restlessly for the next installment on the sea trial.

Another note about propellers.

I expect that one day the supply of Yamaha Performance 3 propellers will dry up. As previously mentioned, I think the Turbo Quest 3 blade 13.125-inch x 15-pitch is probably the best alternative for a Yamaha F70 on a Montauk 17, although I don’t doubt that other props might be suitable. Note that this propeller as sold by BBlades, a shop based in Wisconsin, is offered in two versions – a “stock finish” for $488, and a “lab finish” for $1,008 (hub not included).

I was curious to find out why the big price difference, so I called the company and spoke with the owner-operator Brett Anderson. Mr. Anderson worked for Mercury for many years and at one point was the director of the Mercury Racing Propeller Division. He said the lab finish includes slight thinning of the back side to make a “true wedge”, refinishing the front side if needed, “zero-gram” balancing, and altering the cupping as necessary. The lab finish prop comes with a “satin race buff” finish for maximum speed, but a highly polished finish, which provides better corrosion resistance, is also available.

Mr. Anderson recommended that I obtain a stock propeller through their testing program (currently $60 plus shipping), and they can modify the prop if needed to improve performance. Mr. Anderson indicated that a lab finish could result in a gain of 150-200 RPM at wide-open throttle.

If the Performance Series 3 prop doesn’t work for me, this is the route I will go.

M

PART THREE: FUEL SYSTEM

Before putting the boat in the water, I had to reinstall the fuel system. Fortunately, the fuel connector for my Mercury outboard fits the Yamaha, but the Yamaha owner’s manual recommends installing an external 10-micron fuel filter despite there being a 10-micron filter under the engine cowling. When I purchased the boat, it came with an external fuel filter installed in the splash well just above the hull stencil. Although I have read that this isn’t a good place for such a filter, it served me well there. For most of the last 30 years, I’ve used a RACOR S3213 fuel-water separating filter with a clear plastic drain bowl, and during that time there have been only two problems: One was when I left the filter on for two years before changing it, there was enough corrosion on the filter threads to require a wrench to remove it. The other was that the drain bowl wouldn’t securely thread on to the filter after a few years of use. This is a well-known defect that was corrected by the manufacturer ten years ago (read about it here).

I’ve never had a problem with water contamination, so two years ago I replaced the Racor with an inexpensive in-line filter (Baldwin BF7736) which the manufacturer says is designed to “protect sensitive fuel system components, such as injection pumps and injectors, from damaging contaminants”, but makes no claims to be water-separating, and the manufacturer doesn’t provide a filtration size, so I took this opportunity to reinstall the RACOR filter. Despite having spent more than 30 years above the splashwell, there was very little corrosion of the Quicksilver mounting head, perhaps because the motor had dripped a little oil on it every time the lower unit was raised. The spot where the filter had been installed was now covered by a 3/8-inch-thick transom support plate, so I carefully drilled and tapped the plate for two ¼-inch x 20 stainless steel screws for the reinstall. I generally use something to prevent corrosion and galling when dealing with stainless steel fasteners, especially when fastening dissimilar metals, and in this case I applied anti-seize lubricant that I had left over from another project.

One concern regarding fuel systems that boat owners have argued about for decades is where to locate the primer bulb in relation to the fuel filter. Proponents of putting the bulb downstream of the filter claim this will prevent damage to the filter from high pressures generated by the bulb and protect the check valves in the bulb from being clogged by debris, while advocates of locating it upstream of the filter argue that this will make priming an empty filter easier and avoid damage to the engine from debris released by the bulb should the rubber of which it is made deteriorates. Neither the Yamaha owner’s manual, rigging guide, nor the service manual that I reviewed comment on this, but this recent post suggests that the argument has been settled, at least for Racor filters:

JimH wrote:
The installation instructions for fuel-water separating filters (particularly the filters made by RACOR) usually specify that the filter is to be installed on the suction side of any primer bulb in the fuel hose.

(You can find this post here.)

I was intrigued by this comment since I have been a Racor customer for more than 30 years and had never encountered this instruction. I searched the manufacturer’s website and reviewed their extensive (888 pages!) online catalog , which contains detailed information about all their filters, including installation instructions and diagrams. The term “primer bulb” does not appear in this document; however, Racor markets filters that incorporate built-in priming pumps, like this one. These priming pumps are on the upstream side of the filter, meaning they pump fuel from the tank into the filter.

Note the following Racor installation diagram:



Perhaps this controversy about primer bulb placement exists because Racor recommends that fuel transfer pumps be downstream of the filter to avoid emulsification of water with fuel. Given that fuel transfer pumps aren’t the same as primer bulbs and Racor markets priming pumps that are upstream of its filters, I think one can safely install a primer bulb either upstream or downstream of the fuel filter. Here is what my fuel system looks like now:


I’ve kept the in-line fuel filter for now, but at some point I might replace it with a 100-micron pre-filter to minimize resistance in the fuel system, or perhaps I'll just remove it.

Regarding damage to a fuel filter from over-pressurization by an upstream primer bulb, Racor cautions against pressures above what is rated for the filter, which in my case is 7 psi. Can a primer bulb exceed this pressure? Having some pressure gauges and fittings previously used on other projects, I decided to find out. I hooked up a primer bulb to about one foot of fuel line with a pressure gauge and a ball valve on the other end. When I pumped up the system with air, I couldn’t get more than about 0.5 psi, but when I filled the system with water, the pressure immediately rose on pumping, with the bulb becoming firm at 3 to 4 psi. If I were preparing the engine to run, I would have stopped pumping at this point. I could get the pressure up to 18 psi, but only with a very vigorous effort that I would not have been able to achieve on a boat. Keep in mind that this was a worst-case scenario, with a short run of tubing and pumping against a closed valve. I’m comfortable that I won’t be damaging my filter by using an upstream primer bulb. (By the way, even if you have a primer bulb downstream of your external fuel filter, you are still upstream of the filter under the cowling.)

M

Figure 5 shows the fuel hoses being used have a gray external covering. However, the hoses do not appear to have the "metallic" gray appearance that was a birthmark of hoses that had a notorious history of becoming blocked when a liner to the inner portion became detached from the outer hose material when the hose was used with gasoline-ethanol blended fuels. The legacy of these bad fuel hoses has tended to associate the color gray in fuel hoses to be somewhat suspect. Perhaps you can give details about those hoses.

Also, on the topic of fuel hoses, I was very surprised at the recent cost of properly rated fuel hose that complies with the latest federal regulations about permeability of the hose, and with ratings for tolerance of gasoline-alcohol blended fuels. While WEST Marine might not be the cheapest source, selling fuel hose at $10 per foot seems rather crazy-expensive. Compare at

https://www.westmarine.com/shields-rubber-3-8inch-i.d.-series-368-low-permeation-marine-fuel-hose-10378032.html

As for where the primer bulb ought to be located relative to a RACOR fuel-water separating filter, I cannot recall exactly from years ago where I found some literature from Parker that recommended the primer bulb be placed downstream of their filters. However, there are many instances in Boston Whaler boats that are pre-rigged at the factory where the primer bulb is placed downstream of a fuel-water separating filter. Also, putting the primer bulb near the engine seems like a more practical placement.

With today's engines the need for a primer bulb is much reduced, as their fuel systems are not openly-vented to the atmosphere as they were in the heyday of carburetor engines, so once the fuel system has been primed, it remains primed for months and months of non-use as there is no fuel evaporation in the carburetors. I still have a primer bulb on my boat, but at Spring engine start only perhaps one squeeze of the primer bulb will remove any softness in the primer bulb.

Your notes on experiments with creating pressure with a primer bulb are most interesting. Actual testing is the best method to obtain data like that, and to know you could create 18-PSI is very interesting.

Also thanks for the link to the RACOR literature about suspect clear fuel bowls. That topic has come up before, but the literature you found from RACOR makes the situation more clearly presented.

ASIDE
Installing a pressure gauge across the filter element is a recommended method to show the loss of pressure through the filter element which is then used to deduce that the filter media is becoming clogged and needs to be changed. But adding that on a small boat installation would seem a bit extravagant.

CONFESSION
I have an older RACOR with a clear, removable lower bowl, and I have not changed it in years. It is one of those projects I keep thinking about, and I have new filter media, but I just never quite get to.

After years of struggling with fuel hoses obtained at the local sporting goods store, I purchased a Quicksilver 8M0061890 Fuel Line Assembly - 9 Ft. Long with Primer Bulb. Pricey, but money well spent, as the liner doesn’t separate from the rubber when a fitting is inserted, unlike the aftermarket lines I have encountered. I’ve used the Quicksilver assembly for over two years, and it’s holding up well.

I chose to rig my fuel assembly so the primer bulb could be easily held vertically while being pumped; if I were to have installed it after the filter, I would have needed an extra foot or so of fuel line to achieve that. I suspect that boat manufacturers have to deal with many challenges when they rig their boats, including economy of supplies and ease of installation, and I respect them for that, but sometimes their rigging can be improved upon. In lieu of advice from the engine manufacturer, I think the most reliable information about whether the primer bulb can be located before the filter would be obtained by asking the filter manufacturer, and someone seems to have done just that.

Vince MH wrote:
I emailed Parker/Racor and asked that question. Their answer was that it didn't matter. In fact he suggested I put it before the filter so the bulb can be used to fill a new filter.

(You can read that post here).

M

I think you meant to point to only this post:

https://www.thehulltruth.com/8928693-post15.html

You pointed to the entire discussion, and in that discussion there were advocates for the primer bulb to be both upstream and downstream of a fuel filter.

On the topic of creating pressure, one advocate praised putting the primer bulb upstream of the filter because in that position MORE pressure could be created and thus any leaks resulting from that pressure could be detected. This type of testing reminds me of the old joke about a circuit that tests fuses by creating excessive current—which of course causes the fuse to open. Intentionally creating excess pressure in the fuel system to induce leaks seems exactly like the humorous fuse tester proposal.

When a primer bulb is quickly squeezed by a strong hand, a much greater pressure can be created—18-PSI in a recent test—than can be created by the suction of the primer bulb expanding back to its original size. That alone seems to be sufficient cause to NOT put the primer upstream of the filter.

The linked thread fulfills a well-know paradigm that any internet discussion with more than a few posts will contain diametrically conflicting advice.

PART FOUR: ENGINE BREAK-IN

When I took delivery of the boat, I received two sets of break-in instructions. Here is the one in the owner’s manual:


And here is what I received from the dealer:


Note that the manufacturer recommends avoiding wide-open throttle use during the second hour of the break-in, while the dealer strongly recommends it. I reconciled the two sets as best I could and started the sea trial after two hours.

M

PART FIVE: SEA TRIAL

• June 6, 2025; Lewis Smith Lake, Alabama; elevation 510 feet; air temperature 79-degrees-F;
• boat speeds measured by GPS (Humminbird Helix 5); engine speed measured by Quicksilver analog tachometer (not calibrated); aAll values listed are the mean of two runs in opposite directions;
• jack plate raised 1.5-inches (A/V plate 2.5-inches above keel);
• engine trim set to be neutral at 4,500-RPM.

Before beginning the formal trial, I ran the boat at 4,500-RPM and moved the jack plate through its entire range. I only gained about 1-MPH boat speed by jacking up the engine all the way, and this was accompanied by substantial propeller and exhaust noise. This was similar to what I had encountered with my previous engine (see here).

Trial 1 – One person, two batteries in stern, two Mirax aluminum 12-gallon fuel tanks, 7 gallons fuel, two empty ice chests. Estimated total cargo weight 358-lbs.
Trial 2 – Equipment as in Trial 1 plus 10-gallons more fuel and 220 quarts of lake water, (100 quarts in forward ice chest, 120 quarts in chest behind pilot seat). Estimated total cargo weight 874-lbs.

.................................Trial 1                                   Trial 2
Time to plane (sec)             7.0                                        8.9
Speed (mph) @
3,000 RPM                          11.5                                       9.0
4,000 RPM                           22                                         20
5,000 RPM                           28                                         27.5
WOT RPM/speed               6,000/33.5                           5,850/31.5

Additional observations:
- I achieved a WOT RPM close to 6,000-RPM, but I lost 5.5-MPH at WOT going from a two-stroke Mercury 90-HP to the Yamaha F70.
- There was a striking improvement in initial acceleration. I had to firmly grasp the steering wheel when accelerating from idle to keep from falling over. Perhaps this is due to having a lighter, ventilated propeller.
- I typically cruise at 25-MPH, and I’ll be able to do that by running this engine at about 4,500-RPM.
- These speeds are a bit slower than what I have seen previously posted for this boat/engine/propeller combination.

Your comments would be welcomed.

M

I was curious about the 5.5-MPH loss in top boat speed from the 90-HP to the 70-HP.

Using the Crouch Speed Prediction formula as implemented in my Crouch's Calculator, the following inferences can be made:

Assuming the boat weight in both tests was the same, all other influences on engine power output (such as weather) were the same, and assuming the boat speed with the 90-HP was 33.5 + 5.5 = 39-MPH, then the inferred power of the F70 would be 66-HP to reach 33.5-MPH

If the boat weight in the F70 testing were 100-lbs greater due to a heavier engine or other factors, then 70-HP from the F70 would produce the achieved boat speed of 33.5-MPH.

In this comparison the boat weight was inferred to 1,917-lbs and the hull factor was 180.

Cf.: https://continuouswave.com/calculators/crouchCalc.php

I suspect that the cause of the lower boat speed is probably due to the weight increase and the F70 power is closer to 70-HP than at first glance.

The elaborate regimen for engine use during "break-in" seems to be something that has occurred with marine outboard engines using four-stroke-power-cycle designs. For perhaps 100-years four-stroke-power-cycle engines have been used in automobiles, and I do not recall any special conditions imposed for engine speeds in their initial use. I do recognize that marine outboard engine are generally operated at higher power outputs for a greater percent of their operating time than automobile engines will encounter--unless driven be teenagers.

Q1: do you have any speculation why your Yamaha outboard engine manufacturer and dealer both set out specific guidelines for "break-in" operation?

Our 2025 Honda CRV hybrid has a recommended 600 mile break-in procedure. I won't go into the details but the recommendation is to avoid full throttle acceleration, hard breaking, etc. The recommendation is supposedly due to the high output to displacement ratio of most newer engines.

Jefecinco wrote:Our 2025 Honda CRV hybrid has a recommended 600 mile break-in procedure. I won't go into the details but the recommendation is to avoid full throttle acceleration, hard breaking, etc. The recommendation is supposedly due to the high output to displacement ratio of most newer engines.

Thanks for that input. Perhaps the need for specific operating speed during break-in is becoming more common in automotive engines.

Thank you for the rigor and detail included in this thread. You comments will be valuable to me in the future, as I hope to have a 17-foot hull with a four-stroke-power-cycle engine on the transom.

I also read your article on why you chose a F70LA instead of a a much heavier 90 or 100-HP engine for your targeted use, and that not all decision about horsepower need be made for maximum speed at WOT.

I would like to to see more details and pictures of the engine and jack plate.

Q2: at what height has the jack plate been set for day-to-day use of the boat?

Q3: do you think that having the engine slightly farther aft of the transom has an effect on performance?

Q4: if you indeed think the jack plate set back has affected performance, what was the effect?

David--thanks for your interest in this project. You can find much more detail about this jack plate on my Montauk 17, including the answers to your questions, by reading at:

Atlas Micro Jacker hydraulic jack plate on a Montauk 17
https://continuouswave.com/forum/viewtopic.php?f=6&t=7564&p=45599#p44060.

I expect to complete the sea trial on this boat by the end of August, and I will post the results shortly thereafter.

M

[Moderator's note: I changed the URL and link above to point to the entire thread on the installation of the jack plate and its performance, instead of just one of the several posts in the thread.]

When I hooked up the trailer to take the boat out for a spin in the lake before heading for my annual Louisiana fishing trip, I noticed that the tongue weight was much heavier than before the repower. I have an EZ Loader adjustable trailer, and a few years ago I had adjusted it so that the transom is directly over the rear rollers while maintaining the tongue weight at about 175 pounds. Since the recent repower, the tongue weight is 260 pounds.



I believe the definitive treatise for calculating the trailer setup to achieve a specified tongue weight is an article on ContinuousWave (see here), but I just did it empirically by suspending the trailer on concrete blocks, loosening the bolts that secured the axle, moving the axle by tapping the supports with a hammer and block of wood, re-tightening the bolts, removing the blocks, checking the tongue weight, and repeating the process until I achieved the desired tongue weight. This may sound tedious, but it was actually easy to do. With both 11-gallon fuel tanks full and two batteries, I estimated that my gross weight is about 2,000 pounds. I wanted a tongue weight between 5 to 10% of the gross weight, or 100 to 200-lbs.



I added a 42-lbs bucket of kitty litter at the transom to approximate the weight of the second battery with which I usually cruise. Moving the axle assembly forward 5-inches yielded a tongue weight of 185-lbs--close enough.

--M

If your estimated total weight of 2,000-lbs is correct, and your measured trailer tongue weight is accurate, then the amount of tongue weight as a percentage of total towed weigh is then 180/2000 = 0.90 or 9-percent.

The previous tongue weight of 260-lbs was 260/2000 = 0.13 or 13-percent.

When part of the towed trailer weight is transferred to the hitch of the towing vehicle as tongue weight, most of that weight is transferred onto the rear axle of the towing vehicle. There may also simultaneously be a reduction of weight on the front wheels of the towing vehicle. By reducing tongue weight, you most likely also reduced the weight on the rear axle of the towing vehicle while perhaps also increasing somewhat the weight on the front axle, compared to those weights with the higher tongue weight.

If the towing vehicle is a front-wheel drive, losing weight on that axle can reduce traction and affect steering. So decreasing tongue weight can help avoid those problems.

ASIDE: on my rear-wheel drive 1995 GMC Suburban the recommend tire pressure for the front wheels is lower than for the rear wheels, which I believe is done to maintain better contact with the road surface for the front tires and improve steering.

The Yamaha F70 owner’s manual recommends that if the engine cannot be trailered in the normal running position, an additional support device should be used to secure it in the tilt position. I didn’t have any support device, so last month I just tilted the engine up and headed out on the highway. During the 400-mile trip from Birmingham to Cocodrie, Louisiana, I noticed that the lower unit moved down a few inches, but not enough to put the skeg in danger of hitting the pavement.

My fishing partners seemed relieved to see the new engine, and once launched they were impressed with how quickly it started: no priming, no throttle pumping, no smoking,and no roaring. We had no engine-related problems during this five-day trip, but one of my partners commented that this motor had a little less “punch” while getting up on plane.

With four people, 20-gallons of gasoline, two batteries, a trolling motor, fishing tackle, and a full 100-quart ice chest, performance at wide-open throttle was a boat speed of 31 MPH with engine speed of 5,800 RPM, closely matching the previous performance with the boat heavily loaded.

I don’t have any way to monitor fuel flow yet, but gasoline economy seemed about 15-percent better than with my previous engine. I suspect that fuel use would have been less if I had run the engine slower than the 4,500 to5,000 RPM engine speed I used for most of the trip.

The only thing I miss about my old engine was the ability to crank the speed up to 35 MPH once we enter Bayou Terrebonne headed back to the fishing camp. My fishing partners were happy with this trip. (See Figure 9).



One interesting phenomenon observed during this trip was how the boat wake changed as the engine was raised while underway. In Figure 10, the photo on the left (marked A) shows the engine trimed with the anti-ventilation plate just below the water surface. In the photo on the right (marked B) the engine is trimmed is one inch higher, with the anti-ventilation plate now about a half-inch above the water surface. Note that raising the anti-ventilation plate above the surface of the water results in water spraying out laterally from the lower unit. This would seem to be a convenient way to confirm the height of the anti-ventilation plate from the helm. I didn’t notice any change in performance when doing this, but the exhaust noise got a bit louder.



Overall, I am happy with this new engine, so I’m keeping it.

My next project will be to set up an NMEA 2000 network so that I can more closely monitor the operation of the engine.

M

msteinkampf wrote:My next project will be to set up an NMEA 2000 network so that I can more closely monitor the operation of the engine.

I can't offer any advice regarding a Yamaha engine and connecting it to a NMEA-2000 network. There seems to be some peculiarities associated with where you connect to the engine data depending on what type of Yamaha-brand instrumentation you already have. If you solve that puzzle and work out the various dependencies, as I am sure you will be successful at doing, a separate discussion on the topic "Connecting Yamaha engine to NMEA-2000 Network" would be very welcome. I don't understand what the mystery is about it, and I have not seen a good explanation of the why's and the wherefore's.

A few months ago I installed a Garmin ECHOMAP UHD2 93sv connected to the engine via an NMEA 2000 network (you can read the details of how I accomplished this here: https://continuouswave.com/forum/viewto ... =9&t=10083). This allowed me to assess fuel efficiency, as shown in this graph:


These performance curves closely match those published by Yamaha for a boat of similar weight and hull design, the Avid 18 XB, outfitted with a Yamaha F70 and a Talon SS 13-1/8 x 14 propeller (see here: https://yamahaoutboards.com/outboards/1 ... -27-20_alm). A recent fishing trip gave me another chance to evaluate boat performance. I found that in calm water, I could obtain an additional 0.5 MPG by raising the engine so that the ventilation plate was about 2 inches above the water surface.

M

This is a nice re-power article.

And thank you for documenting the trailer [tongue weight change process].