1970 SAKONNET 90-HP

Optimizing the performance of Boston Whaler boats
Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

1970 SAKONNET 90-HP

Postby Kolbert » Tue Mar 02, 2021 12:14 pm

What is a good propeller for a 1970 SAKONNET with a c.1988 Johnson 90-HP with a Anti-Ventilation plate foil extension? The current propeller is an old aluminum three-blade.

I am looking for [acceleration from a standing start].

There is no tachometer or speedometer on the boat--[I can make] just seat of the pants observations [and thus do not have any performance data to report for engine speed or boat speed].

LONG BACKSTORY: Over the past two years, the engine is a little off and pulling up inexperienced water skiers is more of a challenge because, to them, [the acceleration] is not fast enough. To get on plane quicker, I installed a hydrofoil which helps to keep bow down, but robs a lot of top end. so I am now zeroing in on this being the culprit. So time for an upgrade. I have no friends next door with six backup props in different configs for testing.

I have worked on plenty of car and boa engines so I am not a novice. [On the current engine there are new] plugs, fuel filters, and fuel lines. I have rebuilt the carburetors.

[Several non-boating related sidebar topics have been removed from the backstory portion of this post--Moderator]

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Tue Mar 02, 2021 1:45 pm

What is the manufacturer's recommend full-throttle operating range for the engine?

If specified, what is the optimum recommend full-throttle operating range for the engine?

What is the pitch, diameter, manufacturer, and model of the current propeller?

User avatar
Phil T
Posts: 2602
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1970 SAKONNET 90-HP

Postby Phil T » Tue Mar 02, 2021 2:10 pm

To do a competent effort on assessing your engine and recommending changes, you really do need a tachometer.

In addition to JimH's questions, what is the mounting height of the engine? How many empty holes above the top bolt of the engine bracket?
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Tue Mar 02, 2021 2:42 pm

Thank you for streamlining my post. I will be much more succinct.

Per a Michigan Marine chart, a 90 HP Johnson from [2001 to 2006--USE FOUR DIGI has a range of 4,500 to 5,500 and a gear ratio of 2:1. I couldnt find info on an 1988 but have to believe that [these specifications] haven't changed much overall for c.1990 V4. i-Boats showed 5000.

The current propeller and setup was done at the boat dealer when the engine was installed about 20 years ago. The propeller is an OMC, but I have no knowledge of the specs other than "factory." I can check the mounting height tonight.

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Wed Mar 03, 2021 8:21 am

Based on the engine having a gear ratio of 2:1 and being restored to proper tune so it develops its rated 90-HP at the propeller shaft and being able to accelerate to 5250-RPM at full throttle under load, and using an estimate of top speed as 44-MPH, the propeller pitch would probably be 19-inches.

The estimate of 44-MPH top speed is taken from estimates given in the REFERENCE section for the 16/17-foot hull.

For faster acceleration when pulling water skiers, a 17-pitch propeller would probably be useful.

In general a stainless steel three-blade large-blade-area large-diameter propeller without excessive blade rake is likely the best choice.

As PHIL T notes, without the ability to measure engine speed and boat speed with accuracy and repeatability, there is no possible route to propeller optimization.

Also, on an early 16/17-foot hull the OMC engine was probably mounted using the blind-hole method for the lower engine mount holes. A separate article discusses engine mounting height and hole layout. See

Transom Mounting Hole Layout for Shallow Splash Well
http://continuouswave.com/forum/viewtopic.php?f=7&t=5808

The above article also links to two other excellent articles explaining engine mounting problems with shallow engine splash well designs as in the pre-1972 16-foot hulls.

Re using an Anti-Ventilation plate foil extension: Boston Whaler boats with proper set up and with engines of proper weight generally do not benefit from use of these foil extensions. If a foil is to be used the engine mounting height must be properly configured so the foil is running above the water flow around the gear case when the boat reaches hydroplane speeds.

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Wed Mar 03, 2021 8:42 am

Hi Jim,

Thank you for the reply and the link. I took a look at the mount setup this morning and there are 4 holes on the mounting bracket. My engine is bolted thru the top hole. As far as the propeller, I have the original that was dinged on a rock many years ago, but I dont see any markings noting the size and pitch.

Some info that didn't make it thru translation from my original was;
______________
--- I have seen info (once again E-Tec related) with so many different sizes and pitches. Here is a list of the E-Tec props but even this is confusing because some have " (inches) on the first number (diameter?), others on the later (pitch).
13.25x19 Stiletto ADVANTAGE 1
13.5 x 20” Raker
13-7/8" x 19” BRP Viper
13-1/4" x 19” SST (2 holes up)
13-1/4" x 17” Turbo 1
______________

User avatar
Phil T
Posts: 2602
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1970 SAKONNET 90-HP

Postby Phil T » Wed Mar 03, 2021 9:11 am

To determine prop size we use the engine's lower unit gear ratio, wide open throttle (WOT), target speed, hull factor and propeller slip and calcuate the desired propeller blade pitch. The diameter is typically set by the gear ratio.

The reason why you see a list of different size propellors is that size is not universal across brands or even models. The first number is the diameter of the prop. The second number is the pitch of the blade. Due to different blade geometry the pitch size may be different.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

User avatar
Phil T
Posts: 2602
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1970 SAKONNET 90-HP

Postby Phil T » Wed Mar 03, 2021 10:12 am

Here are the results from a propeller calculator:

RPM = 5500
RATIO = 2.00
SLIP = 5
MPH = 43
PITCH calculates to 17.4

Boston Whaler owners have tested dozen of models with dozens of engines. Through this there is a list of prop recommendations for specific Whaler model and engine combination.

The list you posted appears to be the owner recommendation list for the classic Johnson/Evinrude 90hp 2 stroke.

If you are going to pull tubers or skiers, I would select a 4 bladed prop. When doing this selection, owners of 3 bladed props typically use their current size and drop down 2" of pitch in the 4-bladed prop pitch size.

Ditch the foil. This is a bandaid to alleviate the concern of your engine being mounted too low on the transom. Due to the engine being so deep, acceleration is causing excessive bow rise. I will guess the engine is bolted on to the transom using the "blind" holes for the two lower fasteners. This was the traditional method back in the day. In using the blind holes, the engine height can't be changed unless you remove it and redrill the lower holes to use the slots.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Fri Mar 05, 2021 8:28 am

Kolbert wrote:I took a look at the mount setup this morning and there are 4 holes on the mounting bracket. My engine is bolted thru the top hole.


My inference from your narrative: assuming the transom hole layout is in accordance with the BIA recommendation, your engine is mounted in the lowest possible position.

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Fri Mar 05, 2021 8:36 am

Kolbert wrote:Some info [was deleted from the original post]
Yes. See below

Kolbert wrote:...I have seen info (once again E-TEC related) with so many different sizes and pitches. Here is a list of the E-Tec props...


The reason I removed your listing of propellers for use with a different engine on an unspecified boat is that data was not particularly cogent to the engine and boat you are asking about.

For propellers of one manufacturer and one style and a consistent diameter, the pitch markings can be seen as indicating progressive increments or decrements of the propeller's effective pitch. Modern propellers generally do not have a fixed singular pitch, but use a progressive pitch that varies depending on what point in the blade shape you measure.

To find that propellers from another manufacturers using different style or different diameter or different number of blades can be found to produce outcomes similar to a different manufacturer's propeller of different style and different diameter and different number of blades, and that the PITCH number marked on the propeller is different is quite normal.

Engines have different gear ratios, different maximum engine speeds, and different torque curves. The propeller that produces optimum performance with one engine may not be the best choice for another engine with a different gear ratio, a different engine speed range, and a different power or torque curve.

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Fri Mar 05, 2021 8:45 am

Engine data about gear ratio and recommended engine speed ranges is best taken from the OEM owner's manual or user guide for the particular engine model and model year. Variations in data by model year are common with outboard engines, particularly with engines that were manufactured under the regulations for exhaust gas emission levels by the EPA.

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Fri Mar 05, 2021 9:18 am

Hi Jim and Phil,

I appreciate the time and attention to my question. Bringing this info and some of the thread searches I have done gives a clearer picture. Now I know that I have to at least raise my engine from the lowest hole up 1 or 2 depending on which way I want to go. I am checking into a tachometer setup that will help the overall for sure.

My related question centers around moving up the Johnson 90 that has lower blind holes. Several threads here on re-drilling and plugging the blind holes, not a big concern. One thing I have not found is how to account for where to put the NEW blind holes, or if there is an alternate/better setup to switch to. If I go up 2, then the new holes are 1.5" higher. What happens if this isn't the best setup, and the engine needs to go down a hole? Re-drill 3/4" lower to re-set? I don’t want a swiss cheese transom.

Thank you

User avatar
Phil T
Posts: 2602
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1970 SAKONNET 90-HP

Postby Phil T » Fri Mar 05, 2021 9:20 am

While we will not be able to dial in your boat's performance exactly without a tachometer, a worthwhile prop to select is the Enertia.

Many Boston Whaler owners over the years have had very good results contacting Dan's Discount Props. They are very experienced in prop selection and understand Boston Whaler hulls.

http://www.dansdiscountprops.com
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Tue Mar 09, 2021 2:34 pm

I do not understand how to handle one-hole-up or two-hole up engine mounting height in conjunction with the blind hole mounting method. I only want to drill and plug once.

Were I to were to re-power, I would would go with an E-TEC 90. The E-TEC does not use blind holes.

If I re-drill for the current Johnson 90 to go up 2 holes and then have to re-power, I would need to re-drill again?

Would it be best to go with a jack plate?

The jack plate could solve the current question for one-hole-up or two-hole-up engine mounting and also if I re-power.

Am I looking at this incorrectly?

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Tue Mar 09, 2021 6:37 pm

No modern engines use blind hole mounting.

The FAQ explains in detail the preferred solution for locating the lower pair of holes in the transom for shallow splash wells. The preferred solution is to locate the pair of lower engine mounting holes higher than the standard position. You can move the lower mounting hole pair to be 0.75-inches higher. This will make the lowest possible engine mounting position to be one-hole-up.But you can still move the engine to higher mounting positions if you want with this hole layout.

Also see the article on engine mounting on boats with shallow splash wells for comprehension. This article is pinned at the top of this forum.

viewtopic.php?f=7&t=5808

Reread the FAQ for comprehension. I cannot explain it better than the FAQ.

http://continuouswave.com/whaler/reference/FAQ/#Q8

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Tue Mar 09, 2021 6:47 pm

Kolbert wrote:Would [I] be best to go [buy and install] a jack plate?


I have no idea if your boat would be better if you installed a jack plate. I know it will weight more. It will cost more. You will probably never adjust it.

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Tue Mar 23, 2021 2:48 pm

I was finally able to get to the prop this past weekend and it is a Michigan Wheel 13 x 19 (part # 011004) aluminum. Dinged up but not in really bad condition, other than being 20 years old.

The current setup was done for blind holes with a 6" spacing. I will be raising the engine for sure so now the question is 1 or 2 holes up? Haven't found anything concrete on if the std V-4 90 is best up 1 or 2, but when I repower to the 90 E-Tec, 2 up or higher is certainly the best choice. I am trying not to beat a dead topic, but only want to do this process once. Any feedback from others who have re-drilled for their current old 2-stroke 90's would be greatly appreciated.

For drilling, if I [raise the lower engine mounting hole in the transom by only 0.75-inch from the standard location] I need drill at an slightly up-angle and flat grind the washer bottom,.

How much stress does the up-angle create on the fiberglass?

If I [raise the lower engine mounting hole in the transom by only 1,5-inch from the standard location] I can drill a straight hole.

Found a thread at

http://continuouswave.com/ubb/Forum4/HTML/006694.html

and most of the propellers have been discontinued

Thank you everyone for your time to my question.

User avatar
Phil T
Posts: 2602
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1970 SAKONNET 90-HP

Postby Phil T » Tue Mar 23, 2021 7:41 pm

You don't drill the holes to a fixed height. You drill the holes so that the engine can be adjusted in the future.

Look at the diagram in the reference section. You are over thinking this.

We recommend mounting the engine (not drilling) 2 holes up (bottom bolts in the slots), top bolt in the 3rd hole from top when counting down.

Stainless prop, not aluminum.

Do you have a tach? If not,get one installed before proceeding to prop.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

biggiefl
Posts: 897
Joined: Thu Jul 11, 2019 1:31 pm
Location: south Tampa Bay area
Contact:

Re: 1970 SAKONNET 90-HP

Postby biggiefl » Thu Apr 22, 2021 11:25 am

Having owned a few crossflow V4 engine, the maximum RPM ss 5500.

If pulling skiers I would recommend a OMC SST 17-pitch propeller--easy to find on eBay.

You will want a tachometer as the engine might over-rev by a couple hundred RPM at WOT.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Fri Apr 23, 2021 3:52 pm

Thank you for the feedback Biggie. I just received a tachometer and will install it soon. First order of business is moving the engine mounting height higher by two holes.

The SST is an older propeller. I saw a new OMC Viper propeller on an auction website. Dan [recommended] PowerTech propellers in the 13 x 17.

[Solicits from] anyone [ recommendation for] alternative [propellers].

jimh
Posts: 11672
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1970 SAKONNET 90-HP

Postby jimh » Sat Apr 24, 2021 8:19 am

The OMC SST propeller in 17-pitch would be a good place to start with a steel propeller at a very low cost. There are now two very experienced people that have recommended the OMC SST 17-pitch propeller. Why not try one?

The notion that the OMC SST propeller is no longer made does not mean that all existing OMC SST 17-pitch propeller are now useless. They are made of steel. They don't know they aren't made any more. The will work just like they were in the 2021 catalog and still in production.

The notion that a vendor of new propellers has not recommended an OMC SST 17 propeller is probably related to the concept that he wants to sell new propellers, not used propellers. Vendors who sell new propellers have an amazing tendency to recommend new, unused propellers that they offer for sale, rather than telling you to buy a used propeller and try it.

Regarding where the engine lower mounting hole pair ought to be drilled: the options are thoroughly explained in the article

Transom Mounting Hole Layout for Shallow Splash Well
viewtopic.php?f=7&t=5808

Regarding a measurement of force exerted on the fiberglass by an engine mounting bolt: there is no known information about the amount of force. If you are interested in learning the amount of force exerted by a mounting bolt on the fiberglass I recommend you invent some method to measure the force and make some tests.

Most of the force occurs from the tension in the mounting bolts. The tension in the mounting bolts is specified by the engine manufacturer with the torque specification for the tightening of the bolts.

If you have concern about the fiberglass on the inboard side of the transom being crushed, install a larger washer. Or install a thicker and larger washer. Or install a rectangular plate between the upper mounting hole pairs. All of these methods of spreading the tension of the bolt head onto more area of the transom are used, particularly on larger, higher horsepower, heavier engines.

I don't believe there is too much cause for concern with regard to the method recommended by Boston Whaler for mounting engines in shallow splash wells, because with the the lower engine mounting hole pair raised 0.75-inch from standard position. That advice comes directly from Boston Whaler. I don't see any reasonable basis to infer that Boston Whaler thought the method was prone to problems or might cause damage to their boat. If Boston Whaler thought the method was not a good method and should not be used, why would they put out a service bulletin demonstrating the method?

Do not operate the outboard engine with a propeller that is "dinged". Propellers with damage are out of balance. Rotating an out of balance propeller on the propeller shaft puts stress on the propeller seals and bearings.

The optimization of performance with propellers requires that the following data be known with accuracy:
  • the engine gear ratio
  • the maximum permitted engine speed
  • the actual engine speed underway at full throttle measured by an accurate tachometer
  • the boat speed, typically measured now as speed-over-ground with a GNSS receiver
  • the existence of any current in the water which must be accounted for in the measurement of boat speed as speed over ground
The process of optimization occurs by collecting some accurate data by actual on-water testing of actual propellers. The optimization process is not about how many old threads can be found or how many hypothetical propellers are suggested.

Kolbert
Posts: 13
Joined: Tue Mar 02, 2021 10:34 am

Re: 1970 SAKONNET 90-HP

Postby Kolbert » Thu Apr 29, 2021 5:46 pm

Hi Jim,

You and others have been most helpful in answering my questions and pointing me in the proper direction. Not sure where and why this last response, after the propeller part, came from. I have taken your advice and WILL BE MOUNTING MY MOTOR 2 HOLES UP. This was settled as of March 23. I was even planning to document the process to help others, but I guess there is enough info already out there that has been beaten to death.

Hadn't given this thread another thought until I saw Biggie's comment on the prop. I am not one to turn down good advice and when someone new offers some knowledge, WHY NOT ASK A SIMPLE FOLLOWUP QUESTION? Was planning to deal with the propeller concern once the engine was raised AND I get the tach installed, JUST LIKE I SAID IN MY POST. Looking at my post, can't even really tell what it said about the propeller because it was chopped up and regurgitated.

Maybe you believe I have morphed into Morgan who had the question on mounting height and upgrading to a Honda. I can assure you I have much better things to do with my time than invent aliases and phantom motor upgrades to get another angle on a motor mount question. Maybe I will research the fiberglass test and get back to everyone. :-)

Chop this post up however you like. I am just trying not to do the same to my 50 year old classic.