1979 SPORT 15 Raising Engine

Optimizing the performance of Boston Whaler boats
LBC Sport 15
Posts: 6
Joined: Mon Jun 20, 2022 4:19 pm

1979 SPORT 15 Raising Engine

Postby LBC Sport 15 » Mon Jun 20, 2022 4:40 pm

I have a 1979 SPORT [15] with a 2016 HONDA BF50 mounted all the way down. I plan on raising the engine to be mounted two-holes up.

The HONDA BF50 has three water pick-up inlets. Two of them are in a typical location. One is on the underside of the Anti-Ventilation plate. [See Figure 1 added later in the discussion.]

When the engine is raised to be mounted two-holes up, the water pick-up under the A-V plate will be out of the water.

Will engine cooling water be remain sufficient when the boat is on plane?

I have no way to read the engine cooling water pressure.
Mark

1979 Classic 15 Sport with 2016 Honda BF50

User avatar
Phil T
Posts: 2138
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1979 SPORT 15 Raising Engine

Postby Phil T » Mon Jun 20, 2022 5:52 pm

In 20 years, I have not read of this being a problem.

I will [consult] a guru I know and see if there is any merit to your concern.

(edit) I have heard back. No known concern. Proceed to raise it.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

LBC Sport 15
Posts: 6
Joined: Mon Jun 20, 2022 4:19 pm

Re: 1979 SPORT 15 Raising Engine

Postby LBC Sport 15 » Mon Jun 20, 2022 8:41 pm

Phil T wrote:In 20 years, I have not read of this being a problem.

I will raise it with a guru I know and see if there is any merit to your concern.

(edit) I have heard back. No known problems. Proceed to raise it.


That's great news. Thanks a bunch Phil!
Mark

1979 Classic 15 Sport with 2016 Honda BF50

jimh
Posts: 10370
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1979 SPORT 15 Raising Engine

Postby jimh » Mon Jun 20, 2022 8:53 pm

If there is no way to know the engine cooling water pressure, then clearly there is no concern about it. If you were concerned about engine cooling water pressure, you would already have installed a water pressure gauge to monitor it.

Also, if you do not have a value for engine cooling water pressure that is normal or is the absolute minimum needed to maintain engine cooling, you won't know how to evaluate the engine cooling pressure even if you had that information available.

The general guidance with any raising of the engine mounting height is to monitor the engine cooling water pressure to see if the pressure has decreased below any sort of minimum pressure needed.

Without any way to measure engine cooling water pressure and without knowing what the recommended range of engine cooling water pressure should be for normal operation, you will just have to run the engine and watch the engine temperature gauge. And compare the engine temperature readings after raising the engine mounting to the readings before the engine was raised.

If you don't have an engine temperature gauge, then you can just wait for the engine overheat alarm to sound and for the engine to shut down on its own.

LBC Sport 15
Posts: 6
Joined: Mon Jun 20, 2022 4:19 pm

Re: 1979 SPORT 15 Raising Engine

Postby LBC Sport 15 » Tue Jun 21, 2022 1:15 am

Thank you for the input Jim. Yes, I have no way to monitor the water pressure or temp as I only have a tach, voltmeter and idiot lights. I was told by Honda that I can't bring the AV pickup out of the water but was told by an independent tech that [the manufacturer's advice could be ignored] as there was enough pressure at speed on the other two water inlets.

The shop that rigged the motor used the old lower holes and drilled the bracket so raising the motor requires me filling and drilling new holes in the transom. I didn't want to do that if it was for naught. Unfortunately, this is way above my pay grade and I've gotten conflicting opinions from the experts. Thanks again.
Mark

1979 Classic 15 Sport with 2016 Honda BF50

jimh
Posts: 10370
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1979 SPORT 15 Raising Engine

Postby jimh » Tue Jun 21, 2022 9:34 am

Generally in an outboard engine the water inlets for the water pump in the gear case or lower unit casting would all feed into the centrifugal water pump impeller. Usually the inlets are located on the sides of the bullet near the leading edge of the bullet, and are below the level of the impeller. These inlets are probably what you meant when you described their position as "in the typical place."

The pump cannot prime itself by drawing water upward, so generally the impeller must be located below the water line level. In that way, water rises naturally into the pump inlet. If the engine were raised too high and the impeller becomes higher than the water line, there could be a problem. The impeller is usually located above the Anti-Ventilation plate level. Typically at engine start the water line will be above the A-V plate level, the pump will be primed, and cooling water pumping begins. When the boat is on plane, the water pick-ups on the bullet act a bit like a scoop, and the pressure of the water flowing into them pushes the water uphill into the impeller that may now be above the waterline. That keeps the pump working.

It is common that on the lower unit casting there will be an opening around the Anti-Ventilation plate. But that opening may not be associated with the cooling water pump inlet. It may be an opening for outlet of cooling water that is being discharged into the lower unit in order to cool the exhaust passages. Typically in the flow of cooling water, the water pump pushes water to the top of the engine, and from there it flows downward, through all the passages in the water jacket in the engine block, and eventually flows into the midsection to cool the engine exhaust passages.

I looked at some exploded-view drawing of the lower unit for a BF50 engine, but they did not illustrate a water pick-up inlet located below the A-V plate. Not being familiar with that engine, I don't know for certain what sort of function an opening would serve.

dtmackey
Posts: 701
Joined: Thu Sep 28, 2017 9:29 pm

Re: 1979 SPORT 15 Raising Engine

Postby dtmackey » Tue Jun 21, 2022 10:05 am

When Phil reached out to me, I wasn't aware of the 3 water pickups on the Honda lower unit, especially one under the cavitation plate, which is a very unusual place to have a water intake. Very strange that they would do that.

Is this motor a 15-inch or 20-inch shaft? If a 20-inch shaft, I don't foresee a problem [with cooling water flow loss] as the 15 hull can accommodate a high-mounted engine. The old school using a flat edge along the hull bottom does not provide a real life indication of proper mounting, but does give you a starting point. I can attest that a 15-footer with a Yamaha F70 can be run 6-inches-higher than the transom and not have any water intake problems. With the Honda set-up, just watch your water tell-tale stream when you first test the higher mounting position.

Here are several illustrations from others I've talked with that are using high-mounted engines. I've talked with many others, but do not have pictures of their 15-footers.

Image
Image
Image

For my 15 (below), I can leave the motor jacked up four to five inches under all running conditions and even higher when running on plane, jacked up six inches or even higher.

Image

Here it is running on place at a slow cruise at 25 to 30-MPH

Image

Once you have the engine mounting height optimized for your hull and engine combo, then and only then, you can test propellers to to select the best propeller for your set-up.

D-

jimh
Posts: 10370
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1979 SPORT 15 Raising Engine

Postby jimh » Tue Jun 21, 2022 10:18 am

Observation of the flow of cooling water from the cooling water confidence stream nozzle is also a reasonably good indicator of proper water pump operation, and it is significantly less complex than some other methods.

Corollary: the higher the engine is mounted, the more visible the cooling water confidence stream will be.

LBC Sport 15
Posts: 6
Joined: Mon Jun 20, 2022 4:19 pm

Re: 1979 SPORT 15 Raising Engine

Postby LBC Sport 15 » Tue Jun 21, 2022 4:03 pm

Thanks for the good input.

[The 2016 HONDA BF50 engine shaft length] is 20-inches.

[I plan to raise the engine and to monitor cooling water by] keeping an eye on the overboard confidence stream.

The location of the water inlets on the 2016 HONDA BF50 engine are shown in Figure 1.

IMG_2881.jpg
Fig. 1. HONDA BF50 engine cooling water inlet locations.
IMG_2881.jpg (58.59 KiB) Viewed 110 times
Mark

1979 Classic 15 Sport with 2016 Honda BF50

User avatar
Phil T
Posts: 2138
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1979 SPORT 15 Raising Engine

Postby Phil T » Tue Jun 21, 2022 4:07 pm

At two-holes-up the anti-ventilation plate will be slightly below the water surface.

I would observe this at speed rather than be concerned about engine temperature.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

LBC Sport 15
Posts: 6
Joined: Mon Jun 20, 2022 4:19 pm

Re: 1979 SPORT 15 Raising Engine

Postby LBC Sport 15 » Tue Jun 21, 2022 4:55 pm

Phil T wrote:At two-holes-up the anti-ventilaton will be slightly below the water surface. I would observe this at speed rather than be concerned about engine temperature.
Sounds good. I will do that. Thank you.
Mark

1979 Classic 15 Sport with 2016 Honda BF50

jimh
Posts: 10370
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1979 SPORT 15 Raising Engine

Postby jimh » Wed Jun 22, 2022 10:09 am

Thanks for providing an illustration showing the location of the cooling water inlets on the engine lower unit. That water inlet is unusual. I don't recall mention of a water inlet in that location on other engines, such as the engines shown in several illustrations above depicting raised engine mounting heights.

As long as the anti-ventilation plate remains immersed in the water or just at the water level, the inlet on the lower side of the plate will continue to function as a water inlet. I infer that water flowing around the gear case bullet will be deflected upward and toward the inlet on the lower side of the anti-ventilation plate, and that flow should result in good inflow of water at that point.

Water coming off the transom of an outboard engine boat tends to rise upward, so when the boat is on-plane the water level at the anti-ventilation plate will be higher than the water coming off from under the transom. This is why outboard engines can typically always be mounted so their anti-ventilation plate is located higher than the hull bottom at the transom.

LBC Sport 15
Posts: 6
Joined: Mon Jun 20, 2022 4:19 pm

Re: 1979 SPORT 15 Raising Engine

Postby LBC Sport 15 » Thu Jun 23, 2022 6:59 pm

Thanks Jim. That gives me a little more confidence.
Mark

1979 Classic 15 Sport with 2016 Honda BF50