TENDER 11 Four-stroke-power-cycle Engine

Optimizing the performance of Boston Whaler boats
BW11
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Joined: Sat Jul 29, 2023 8:28 am

TENDER 11 Four-stroke-power-cycle Engine

Postby BW11 » Sat Jul 29, 2023 8:43 am

Give me advice [on re-powering a c.1981 TENDER 11 with a modern four-stroke-power-cycle engine].

BACKSTORY

On my c.1981 TENDER 11 I need to replace a 25-year-old Johnson 15-HP engine. I may buy a 15-HP or 20-HP SUZUKI engine. I have no experience with modern four-stroke-power-cycle small outboard engines.

My TENDER is mostly used by my teenage children for angling in the [Atlantic Intracoastal Water Way]. [The usual crew and gear are]
  • two teenaged childrem
  • cooler
  • cast net
  • fishing poles
  • fuel tank
  • and other miscellaneous gear

ASIDE: The TENDER 11 was powered by an Evinrude 18-HP engine before the Johnson 15-HP was installed.

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Phil T
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Location: Was Maine. Temporarily Kentucky

Re: 4 stroke power for 11’ tender

Postby Phil T » Sat Jul 29, 2023 12:07 pm

Check the weigh of the 15 and 20 and then add the additional weight to what you have in the boat.

You may find you need to shop across brands to find the least heavy.

Shop dealers hard, prices vary a lot.
1992 Outrage 17
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Member since 2003

BW11
Posts: 4
Joined: Sat Jul 29, 2023 8:28 am

Re: 4 stroke power for 11’ tender

Postby BW11 » Sat Jul 29, 2023 4:27 pm

The Johnson 15-HP engine weighs 76-lbs. The SUZUKI 15 and 20-HP engines weighs 97-lbs.

The extra [21]-lbs seems manageable, but I have concern that a four-stroke-power-cycle engine won’t perform the same as a two-stroke-power-cycle engine for getting the boat on a plane.

I am not concerned at all about fill-throttle boat speed. I am concerned about the need for the boat to easily get on plane and stay on plane.

frontier
Posts: 206
Joined: Tue Feb 09, 2016 8:26 pm

Re: TENDER 11 Four-stroke-power-cycle Engine

Postby frontier » Sun Jul 30, 2023 1:37 pm

The classic Standard 11 Tender (tiller steering) weighs 210-lbs and is factory rated for 10 HP maxium.

The classic Sport 11 with remote steering console weighs 250 lbs and is factory rated for 20 HP maximum/

Q3: which model do you have?


To match the old two-stroke-power-cycle engine's low weight and high torque at low engine speed will be hard.

The TENDER 11 hull is very light weight.

I owned an old classic 13-foot with a weight of 340 lbs. That boat had a Mercury two-stroke-power-cycle engine rated at 9.8-HP. That engine was fine with a light load.

BW11
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Joined: Sat Jul 29, 2023 8:28 am

Re: TENDER 11 Four-stroke-power-cycle Engine

Postby BW11 » Sun Jul 30, 2023 3:19 pm

[The TENDER 11 that is the topic of this discussion is] a tiller model.

In my opinion the 15-HP two-stroke-power-cycle engine is a perfect engine for a TENDER 11. I realize the TENDER 11 is only rated for 10-HP.

My TENDER 11 planes efficiently. The TENDER 11 boat has a maximum boat speed of around 23-MPH, and the boat is easy to control.

Q1: [How can you get that same outcome] with a four-stroke-power-cycle engine?

I’m concerned that a 15-HP four-stroke-power-cycle engine will not get a TENDER 11 onto plane, but a 20-HP four-stroke-power-cycle will turn a TENDER 11 into a 35-MPH bullet.

frontier
Posts: 206
Joined: Tue Feb 09, 2016 8:26 pm

Re: TENDER 11 Four-stroke-power-cycle Engine

Postby frontier » Sun Jul 30, 2023 4:06 pm

With the Mercury or the Tohatsu or the Suzuki engines, the 15-HP engine and the 20-HP engine are the same weight and use the same power head; they [may] have different fuel delivery systems.

A reason a tiller-controlled boat is rated for a maximum power at half the rated power of the same boat with remote steering control is due to [the improved] control and the [better] safety [that occurs with remote steering compared to tiller steering].

[Also, a boat whose engine is steered by] remote is more forgiving if you have an operator failure.

No matter what engine: always wear the engine safety shut off switch lanyard. {Moderator's note: this is a federal regulation now for an 11-foot boat.]

jimh
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Re: TENDER 11 Four-stroke-power-cycle Engine

Postby jimh » Sun Jul 30, 2023 6:15 pm

The general opinion regarding the difference between a two-stroke-power-cycle engine and a four-stroke-power-cycle engine with regard to an outboard propulsion engine on a boat is the classic two-stroke-power-cycle engine delivers its rated power over a wider engine speed range than the typical modern four-stroke-power-cycle engine of the same engine block displacment.

To get the same engine power output over a wide range of engine speed operation that exists in a two-stroke-power-cycle engine when using a four-stroke-power-cycle engine, there are generally two approaches:
  • use significantly larger displacement, or
  • used forced induction, such as supercharging or turbocharging.

BW11
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Joined: Sat Jul 29, 2023 8:28 am

Re: TENDER 11 Four-stroke-power-cycle Engine

Postby BW11 » Sun Jul 30, 2023 7:14 pm

I probably will have to settle for [buying a four-stroke-power-cycle engine with] significantly larger displacement [than the current two-stroke-power-cycle engine on the TENDER 11] given those two options [for maintaining the same rated power output over a wide range of engine speeds].

To anyone with experience with a TENDER 11 powered by a modern four-stroke-power-cycle outboard: give me advice [on re-powering a c.1981 TENDER 11 with a modern four-stroke-power-cycle engine].