16 SL Re-power at some future time

Optimizing the performance of Boston Whaler boats
WillWhaler
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16 SL Re-power at some future time

Postby WillWhaler » Mon Sep 07, 2020 10:04 am

In the future [I will re-power my 16SL] and get rid of my [1989 YAMAHA 90-HP two-stoke-power-cycle engine] even if the engine is still running. A time will come for a new engine.

I will probably NOT choose a modern 90-HP four-stoke-power-cycle engine. I consider them too heavy for a 1991 16 SL boat. [When a 1991 16SL was made] a 90-HP weighed 350-lbs and not 450-lbs or more.

I'm looking at the following engines:
—Yamaha F70
—Mercury 60
—Mercury 75

What engine do readers recommend?

Would 60-HP be enough?

Thanks—Michael.
Last edited by WillWhaler on Mon Sep 07, 2020 11:31 am, edited 1 time in total.

jimh
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Re: 16 SL Re-power at some future time

Postby jimh » Mon Sep 07, 2020 10:22 am

Give us the weight of the three engines you are considering.

I would not just “get rid” of the Yamaha 90. There should be strong interest in that engine by buyers. It is a classic engine with a great reputation. Selling it should be no problem and should bring a good price.

WillWhaler
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Re: 16 SL Re-power at some future time

Postby WillWhaler » Mon Sep 07, 2020 11:30 am

Thanks jimh.

[The Yamaha 90] still works but is really old and in not-so-good condition. The power trim doesn't really work anymore, and the engine is very heavy to lift. The engine cannot be blocked in lifted position [due to] broken brackets. [There is] lots of corrosion in the streering bracket.

I paid 1,000€ for it seven years ago, and I would sell it for half the price today.

Concerning weights, both Yamaha F70 and Mercury 60hp are 118-kg or 260-lbs and the 75hp is 360-lbs.

The local Mercury retailer has two Dauntless 15 boats with the 60-HP; they hardly reach 30-nautical-miles-per-hour with one person on the boat and 25-nautical-miles-per-hour with four people.

I believe [a 60-HP] will be too small for my 16SL; the 16SL is 150 to 200-lbs heavier than the Dauntless—without accounting for any water in the foam.

Any thoughts will be appreciated.

frontier
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Re: 16 SL Re-power at some future time

Postby frontier » Mon Sep 07, 2020 8:38 pm

The 1985 through 2007 Yamaha 90-HP two-stroke-power-cycle outboard is one of the best outboards ever made. Find a good factory trained Yamaha shop and fix yours. Or, find a good used one. Lots of them out there.

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Re: 16 SL Re-power at some future time

Postby Saukit » Mon Sep 07, 2020 11:38 pm

Are the 70-75 hp models you're looking at any lighter than the comparable 90 hp? I have considered repowering my 16SL but after some admittedly brief research, most of the 75 hp models seem to use the same powerhead as the 90 hp. They're not any lighter.

The 16SL would greatly benefit from any weight you can remove from the stern.

WillWhaler
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Re: 16 SL Re-power at some future time

Postby WillWhaler » Tue Sep 08, 2020 3:23 am

Thank you all. I won't refurbish my old Yamaha. Even if it's a great engine, it's really noisy and it has a poor fuel economy. I'm using this boat mostly for fishing and trolling, and it's definitely not the best engine for this even if I find this to be a fantastic unit.

The 70 and 75-HP engines I'm looking at the moment are either the same weight as my actual 90-HP, or heavier by 80-lbs or so.

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Re: 16 SL Re-power at some future time

Postby jimh » Tue Sep 08, 2020 9:03 am

Buy a YAMAHA F70a.

Move the engine cranking battery out of the stern and to amidships. Order longer main battery cable of proper heavier wire gauge.

Relocate any other weight in the stern to be more forward as much as possible.

I think you are in Europe where gasoline fuel costs about four times more than in the USA at the moment. Here we are buying gasoline for $2 per gallon or less. At that price gasoline is effectively free—or at least nothing to worry about in comparison to the cost of a new Yamaha outboard engine.

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Phil T
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Re: 16 SL Re-power at some future time

Postby Phil T » Tue Sep 08, 2020 9:49 am

Will--I suggest you revisit outboard engine manufacturer websites and review published engine weights.

Mercury 90hp FourStroke......359 lbs
Honda 90 Four Stroke...........359 lbs
Suzuki DF90A.......................343 lbs
Yamaha F90..........................353 lbs

I recall Honda was the one brand that had a very heavy 90hp offering but that was a long time ago.

CF:
https://www.mercurymarine.com/en/us/engines/outboard/fourstroke/75-150hp/
https://marine.honda.com/outboards/motor-detail/BF75-90-100#specs
http://www.suzukimarine.com/Product%20Lines/Outboard%20Motors/Products/DF90/2012/DF90A.aspx
https://yamahaoutboards.com/en-us/home/outboards/115-50-hp/f115#specs-compare

Of the 12 16SL owners I am aware of, ALL of them have a 90hp engine.

Several have installed trim tabs to help with the boat attitude.
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WillWhaler
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Re: 16 SL Re-power at some future time

Postby WillWhaler » Tue Sep 08, 2020 9:55 am

Thanks for your advice. Indeed I was thinking about moving the battery in the front-right console (the 16SL has two consoles). You are completely right about my location, I'm living in France and fuel cost is a shame. At the car fuel pump we pay approx. 1.50€/l (that is 6.7USD/Gal.) and in the harbor where only boat can refill it is nearly 2€/l (8.9USD/gal). So as you understand, fuel economy counts a lot.

I believe that the Yamaha is indeed a good choice and my number-one today, but if I find a decent Mercury 75 or 80-HP, even if much heavier, I'll seriously consider it.

WillWhaler
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Re: 16 SL Re-power at some future time

Postby WillWhaler » Tue Sep 08, 2020 9:59 am

Phil, thanks for the correction. I have to admit that I'm not used to talk about in lbs instead of kg's ! I did the conversion improperly. My 90hp weights 118kg at the moment, ie. 260lbs, and I'm afraid that the 350lbs of newer engines might be detrimental to the boat behavior...

Even if it doesn't support my idea of downgrading my engine to a 70-HP, it is good to know that all the 16SL that are seen today still run a modern 90-HP engine apparently without any obvious problem.

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Phil T
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Re: Re-powering my 16' SL

Postby Phil T » Tue Sep 08, 2020 11:29 am

I recommend to all owners planning a repower to simulate the new weight in the splashwell before buying new engine.

Take current engine weight, future engineweight, calculate difference. Use bags of sand, water etc and place in splashwell and drive boat around. Observe trim, static position.

Most 16 SL owners add tabs to help get bow down.

High mounted engine and 4 bladed prop helps too.
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Re: Re-powering my 16' SL

Postby biggiefl » Tue Sep 08, 2020 1:03 pm

Your engine is more equivalent to 80hp. If you think shaving 3-4mph from top end is OK, the F70 should do well. The savings in fuel will be amazing, especially if you do a lot of slow speed driving.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

WillWhaler
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Re: Re-powering my 16' SL

Postby WillWhaler » Wed Sep 09, 2020 3:55 am

Phil T wrote:I recommend to all owners planning a repower to simulate the new weight in the splashwell before buying new engine.

Take current engine weight, future engineweight, calculate difference. Use bags of sand, water etc and place in splashwell and drive boat around. Observe trim, static position.

Most 16 SL owners add tabs to help get bow down.

High mounted engine and 4 bladed prop helps too.


Yep, you're absolutely right, this is what I am planning to do indeed ...

WillWhaler
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Re: Re-powering my 16' SL

Postby WillWhaler » Wed Sep 09, 2020 3:57 am

biggiefl wrote:Your engine is more equivalent to 80hp. If you think shaving 3-4mph from top end is OK, the F70 should do well. The savings in fuel will be amazing, especially if you do a lot of slow speed driving.


that's what I thought indeed. I don't know if it's true but I am making this assumption too ...

biggiefl wrote:If you think shaving 3-4mph from top end is OK, the F70 should do well. The savings in fuel will be amazing, especially if you do a lot of slow speed driving.


Yes, that would be fine indeed if I only ride 28kt instead of 32kt ... not a big deal especially as I'm doing a lot of trolling...

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Re: 16 SL Re-power at some future time

Postby biggiefl » Wed Sep 09, 2020 12:43 pm

I have owned that engine [Moderator's note: here I assume "that engine" is intended to mean a Yamaha 90-HP classic two-stroke-power-cycle engine; hereafter I substitute for "that engine" with the inference I have made] and have compared the performance of [a Yamaha 90-HP classic two-stroke-power-cycle] engine on Montauk boats over the decades; in my opinion [a Yamaha 90-HP classic two-stroke-power-cycle] engine is around 80-HP or more. On a classic Montauk with [a Yamaha 90-HP classic two-stroke-power-cycle] engine the boat speed maximum is 41-MPH. An OMC 90-HP will do about 45-MPH. A 70-HP is around 38-MPH. This puts [[a Yamaha 90-HP classic two-stroke-power-cycle engine] and an early E-TEC [90-HP] engine in the 80-HP range based on top speed.

The new F70 is about the same weight as your 90 and will probably do closer to 30-nautical-miles-per-hour boat speed.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

WillWhaler
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Re: Re-powering my 16' SL

Postby WillWhaler » Thu Sep 10, 2020 3:30 am

biggiefl wrote:I have owned that engine ...


Interesting feedback. When you mean 41-MPH on a Montauk, you mean miles and not nautical miles, right ?

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Re: 16 SL Re-power at some future time

Postby jimh » Thu Sep 10, 2020 7:29 am

Boat speeds are usually given in statute miles per hour (MPH) on the forum because small boats are usually operated close to land or on inland lakes, and they do not make international ocean voyages with weeks at sea with no land in sight.

Ocean-going ships use nautical miles to track the distance and speed of their ship underway, based on the relationship to latitude: one minute of latitude is one nautical mile—that is the historical definition.

A dictionary definition of nautical mile says: “a unit used to measure distance at sea.

Exactly when a small boat becomes “at sea” is perhaps entirely in the mind of the boat’s master.

For example, Lake Michigan is roughly 310-miles long and 110-miles wide, so one might feel they were “at sea” out in mid-Lake, but statute miles are still used.

Boat speeds that are not in MPH are clearly indicated with what distance unit is being used to avoid misunderstanding.

WillWhaler
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Re: 16 SL Re-power at some future time

Postby WillWhaler » Thu Sep 10, 2020 9:26 am

jimh wrote:Boat speeds are usually given in statute miles per hour (MPH) on the forum because ...
Thanks for these explanations—very different to the common practice in Europe or at least in France, when the speed of anything going on the water is generally given in knots, i.e. nautical miles per hour. Even for a small fishing boat or a windsurfing board, we always use kt and never use KPH (kilometers per hour). Good to know for the next conversations with you guys.

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Re: 16 SL Re-power at some future time

Postby jimh » Thu Sep 10, 2020 9:32 am

Ship speeds in regulations for inland waters are generally always given in statute miles, even on the Great Lakes where ships from the ocean routinely navigate.

For boating on some small inland lake, nautical miles as a distance unit seems a bit too “salty.”

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Re: 16 SL Re-power at some future time

Postby WillWhaler » Thu Sep 10, 2020 9:41 am

I found that someone did the same conversion that I plan to do, unfortunately he did not answer the messages. Cf.: http://continuouswave.com/forum/viewtopic.php?f=7&t=1647

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Re: Re-powering my 16' SL

Postby cbards » Thu Sep 10, 2020 11:33 am

My 16 SL has a 1997 Honda BF90 engine. I relocated the battery to the starboard console to reduce weight in transom. This made a big difference. I run a stern lifting Power Tech SCD3 stainless propeller. [Boat speed at maximum throttle is] 40-MPH with lower weight load and 36-MPH with medium weight load. I raised the engine [mounting height] to highest setting--this change made the biggest effect on performance. The boat performs great without trim tabs.

Also consider the newer Honda BF100, same weight as the BF 90. However 100-HP will exceed the [boat's] maximum power rating.

WillWhaler
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Re: Re-powering my 16' SL

Postby WillWhaler » Thu Sep 10, 2020 12:02 pm

cbards wrote:My 16 SL has a 1997 Honda BF90 engine...


Good to know. If I go for a heavier engine, I plan to relocate the battery in the driver console indeed.

I don't know anything about propellers and I have to admit that I'll have to learn.

When you say that you raise the engine to the highest setting, how high is it?

Is the anti-cavitation plate higher than the lower edge of the keel ?

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Re: Re-powering my 16' SL

Postby Phil T » Thu Sep 10, 2020 12:08 pm

The standard starting distance is 1 to 1-1/2 inches above the keel. This typically translates to the top bolt in the engine bracket using the 3rd hole, counting down from the top. This mounting height is described as "two (empty) holes up".
see http://continuouswave.com/forum/viewtopic.php?f=7&t=739

For the 16SL, owners recommend the engine being mounted higher than this, 3 holes up or more.
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Re: Re-powering my 16' SL

Postby biggiefl » Thu Sep 10, 2020 12:37 pm

I mount all my engines all the way up and test them. Most stay all the way up or about 2" above the keel.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

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Re: Re-powering my 16' SL

Postby cbards » Thu Sep 10, 2020 1:52 pm

After raising the motor i verified the correct height by observing the anti ventilation plate on waters surface at planing speeds. The lower set engine caused lots of drag and slowed it down significantly. The 16SL is a great little boat once you get its performance tuned in.

One more note: the original 21-gallon in-floor fuel tank was replaced with a 17-gallon tank that was pushed forward in the cavity.

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Re: Re-powering my 16' SL

Postby WillWhaler » Fri Sep 11, 2020 6:14 am

Thank you all for these replies, very interesting. I believe my engine is definitely not as high as you recommend. I'll give a look at it next time I go to the harbor.

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Re: Re-powering my 16' SL

Postby Saukit » Sat Sep 12, 2020 2:34 pm

cards—where did you get the 17-gallon tank?

I have a 1992 16SL with the original tank. I may have to replace it before long. I don't need the full capacity of the current tank. [A 17-gallon tank] sounds like a great solution for reducing some weight at the stern.

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Re: Re-powering my 16' SL

Postby jimh » Sat Sep 12, 2020 4:31 pm

If you want to save the weight of four gallons of gasoline (about 25-lbs) then just fill the 21-gallon tank to only 17-gallons.

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Re: Re-powering my 16' SL

Postby WillWhaler » Mon Sep 14, 2020 2:17 am

Saukit wrote:cards—where did you get the 17-gallon tank?


It took me several years to find a suitable tank to replace my corroded aluminium tank, and I have to say that I regretted every single day the day when I trusted someone who told me to throw away my original tank and to put a plastic one instead. The shape of the tank location in the 16SL is really unconventional and it was a pain to find a suitable non-custom tank on the market. I did find it at CAN-SB, an Italian plastic manufacturer. Not a problem for me as I'm in France. I won't probably be able to re-use the original 16SL filling port and I'll have to use the floor opening for refilling, but I'm OK with this.

The right model I found is the SE2088 reference : https://cansb.com/en/product/se2088-03-05-004-large-capacity-fuel-tank-lt-54/

Less than 200USD delivered from Italy to France. Won't probably be easy to procure in the USA ...

You can surely have your original tank modified and shortened to bring weight to the bow, but It will cost you a lot ...

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Re: 16 SL Re-power at some future time

Postby WillWhaler » Mon Sep 14, 2020 4:41 am

Let's continue talking about engine height. I did check my current engine level yesterday and based on your recommendations it seems really too low. The anti-ventilation plate is clearly below water and there is a lot of water splashing around the engine, that creates lot of drag.

Engine is located one-hole-up [from lowest position] of four possible positions. Shall I raise it by one-hole or two-holes?

[Raising from one-hole up to three-holes up] means mounting at the highest possible levels.

The old Yamaha 90-HP engine accelerates to 5,000-RPM and boat speed is about 31-nautical-miles-per-hour or 36-MPH.

See picture below and video here https://youtu.be/STEg63eexsk

20200913_080517-3.jpg
20200913_080517-3.jpg (117.98 KiB) Viewed 16049 times

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Re: Re-powering my 16' SL

Postby jimh » Mon Sep 14, 2020 6:45 am

Here is a photo of my Yamaha 70-HP engine running on plane.

Image


The A-V plate is more visible than in your image.

How far up the engine mounting can be raised will depend on the propeller is use. In the photo above the propeller was a Yamaha three-blade steel propeller, a standard propeller from them.

WillWhaler
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Re: Re-powering my 16' SL

Postby WillWhaler » Mon Sep 14, 2020 7:51 am

jimh wrote:Here is a photo of my Yamaha 70-HP engine running on plane...


Thanks Jimh. I have a three-blade propeller, I believe that it's the OEM propeller sold with the engine and looks like aluminium painted in white. As I may replace the engine I will likely not change its mounting height, but the discussion is important for the next engine.

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Re: Re-powering my 16' SL

Postby cbards » Wed Sep 23, 2020 9:51 am

[I cannot inform on the source of the replacement 17-gallon fuel tank I mentioned in my September 10, 2020 post because] I purchased the boat with the replacement tank [already installed].

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Re: 16 SL Re-power at some future time

Postby jimh » Wed Sep 23, 2020 10:21 am

Since the 16 SL boat will not be repowered at this time, I don't think it is particular useful to discuss the engine mounting height and propeller selection for the new engine that will be purchased in the future. Perhaps when the new engine is purchased, a new thread can be begun to discuss how high to mount the new engine and what propeller will be most useful on the new engine. The ability to use very high engine mounting height depends on the particular propeller being used, and the shape of the outboard engine gear case and the location of water pick-up inlets on the gear case also affect the ability to use high engine mounting heights.