Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Optimizing the performance of Boston Whaler boats
OregonWhaler
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Joined: Sun Sep 25, 2016 11:53 pm

Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby OregonWhaler » Tue Oct 18, 2016 5:55 am

Hello. This is my first post on this forum. I'd like some help in determining if I should raise the outboard 0.75-inch or 1.5-inch on our Sport GLS 15.

My wife and I were recently gifted her father's 15 Sport GLS. Other than the trips to the mechanic for annual winterizing and spring commissions it mostly sat in his garage for the last 10 years, so we finally convinced him to let us move it out here where it will hopefully get more use.

Here's the moment it rolled onto our block:
Boat_delivery_web.jpg
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Overall it seems to handle nicely and isn't too skittish at WOT, but I do have a couple of interrelated questions and concerns:

  1. The boat gets on plane and behaves itself when the motor is trimmed all the way in, but will immediately start to porpoise if I trim out slightly - even after just a few quick pulses 'up' on the power trim. This seems to be the case regardless of the conditions, as I experience it on both calm, glassy days and on the windy and choppy days this season.
  2. The sideways spray off the outboard looks unusual to me. But is this perfectly normal? The spray, coupled with the porpoising when trimming up, has me wondering if the [2002 Mercury 50 FOURSTROKE] engine is mounted too low? Here is a video I had a friend shoot the last time I took the boat out for a run--with the motor trimmed in. https://youtu.be/TxvQ4uVZ9v8 Sorry it doesn't include footage of the AV plate.
  3. The lower motor mounting bolts sit too close to the radius of the splash well and this has caused some small localized gel coat stress cracks in their current location -
    splashwell_web.jpg
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    .
    This is similar to the concerns raised in this dealer bulletin http://continuouswave.com/whaler/reference/bulletin84-10.html I plan to have the lower mounting holes re-drilled at least .75" higher, but wonder if I should go as far as 1.5" higher - to move the lower bolts as far from the splashwell as possible. My only concern is that drilling the lower holes 1.5" higher will also set the new "bottom" (lowest) mounting position for the motor at 1.5" higher than it is currently - leaving me at a "point of no return" in the event that 1.5" proves to too aggressive of an outboard height increase.

I hope I am making sense.

Unfortunately I can't currently take a photo of the AV plate relative to the bottom of the transom, as the motor has been removed in preparation for working on the splashwell. I should have thought of taking a photo sooner. In the meantime, here is a photo showing which holes in the upper and lower group are currently being utilized.
Outboard_Mount_web.jpg
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Any thoughts, suggestions, or testimonials (ideally from 15-foot hull owners) concerning the outboard splash pattern, and where to drill the new lower mounting holes (.75" vs 1.5" higher) would be greatly appreciated. I don't have a driveway or garage at my home, which means I have to pay my boat yard each time I want to adjust/experiment with the outboard height. Furthermore, the re-drilling of the new lower holes is a one shot deal - so I really want to try and get this right the first time.

Please note that adding a jack plate isn't an option right now - I don't want to put too much money into this.

Thanks for any help you can offer!

Anthony
Last edited by OregonWhaler on Tue Oct 18, 2016 12:44 pm, edited 2 times in total.
1992 Sport GLS 15

jimh
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Re: Engine height: 1992 Sport GLS 15' with 2002 Mercury 50 HP 4-stroke EFI

Postby jimh » Tue Oct 18, 2016 9:43 am

The previous engine mounting was in the lowest position. This probably accounts for the big spray generated by the gear case. Low mounting also tends to accentuate the tendency for the bow to oscillate on plane (or porpoise). Raising the engine at least one-hole is recommended. It is difficult to predict if two-holes up will be better. It depends on the propeller and how well it will tolerate a higher mounting.

The location of the present holes in the transom appears to conform with the usual BIA engine mounting hole layout. I don't know that you must relocate the lower hole. If you do decide to elevate the lower mounting hole location, just raise it 0.75-inch. That will require the engine always be mounted one-hole-up at a minimum. The appearance of small stress cracks on the gel coat around the bolt head on the lower mounting bolts is probably not a big concern. Perhaps they were caused by over-tightening of the mounting bolts and are just a cosmetic defect. Is there any sign of compression of the transom in that location?

To create a new set of lower engine mounting holes in the transom will require that the existing lower holes be properly repaired. It seems like a lot of work if the defect is only cosmetic.

Since the boat is a 1992 vintage, it was most likely not delivered by the factory with the engine mounted and rigged. The transom was probably drilled by a dealer who sold and installed the original engine. The dealer probably should have drilled that lower hole on a slightly upward angle from the stern toward the splash well to create just a bit more room. When the 2002 engine was fitted, perhaps the installer over-tightened the mounting bolts, creating the stress cracks.

jimh
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Re: Engine height: 1992 Sport GLS 15' with 2002 Mercury 50 HP 4-stroke EFI

Postby jimh » Tue Oct 18, 2016 9:47 am

Also, the tendency for the bow to oscillate when on plane is being aggravated by the increased transom weight of the heavier four-stroke-power-cycle engine. You should consider relocating the engine starting battery and the fuel tank to amidships to get some weight out of the stern of the boat.

Also, the cable for the SONAR transducer runs through the transom splash well drain. This is often seen, but I think it is a sloppy installation method. The hole is a drain, not a wire access conduit. But that's just my take on it.

jimh
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Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby jimh » Tue Oct 18, 2016 11:02 am

Also--great first post. Welcome to the forum--jimh

flymo
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Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby flymo » Tue Oct 18, 2016 11:34 am

Welcome aboard Anthony! Great boat, nice you were able to give it a home where it will get some use.

For reference, my 1989 15-footer is powered with a Yamaha F70; it is mounted "two holes up" or two holes above the lowest possible mounting point. My lower bolts are drilled at an upward angle, which was Whaler's recommendation at the time for 15s. I'm glad I didn't have to do the drilling myself, but whoever did it made a nice job of it.

I see you have already removed the motor. From the picture, your existing holes seem to be drilled about 1-inch higher than standard, and then they used the top holes to mount. That nets out to your motor being mounted about 1/2-inch lower than mine--although not all motors have exactly the same length legs. It is likely you'll be able to mount your motor at least one hole higher, possibly more, but I'd strongly recommend reinstalling the motor and experimenting rather than drilling. The gel coat cracks are completely cosmetic and nothing to worry about, so you if you find a sweet spot, you may or may not want to bother to re-drill--especially since you don't want to have too much money into it.

One other factor that will affect the porpoising is the propeller--if you have a bow-lifting prop installed, that will also exacerbate it.

Flymo
Last edited by flymo on Wed Oct 19, 2016 9:35 am, edited 1 time in total.

OregonWhaler
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Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby OregonWhaler » Tue Oct 18, 2016 1:31 pm

Thank you to both of you for the swift replies!

Flymo - if I can ask, how did you determine that the existing holes are drilled 1" higher than standard? Are you referring to both the upper and the lower holes? I am not disagreeing, I am just curious to know how you calculate/guess this. At the risk of pushing my luck Would you mind posting photos showing how and where your holes are drilled (ideally a photos of both sides of the transom). It is really helpful if I can bring proven/working examples to the yard.

JimH - the boat yard had the same theory/concern about the lower holes being over-tightened. I don't recall the transom looking compressed at the lower holes, but the area immediately surrounding each lower of the aluminum brackets does looks "crushed" due to the cracking. There is another area where the original mounting holes were (for the original motor) that clearly shows the footprint of two washers. Those are compressed but not cracked.

To address the cracking at the current lower holes, I have the option of a simple gel coat repair (and the yard suggested grinding the lower lip of the little aluminum mounting brackets to eliminate the sharp 90 degree angle), but understandably the boat yard explained "we can't guarantee the cracks won't reappear next year, due to holes' proximity to the splash well radius." So, I have the option of either a cosmetic patch repair, or spending a little more to attempting to address the (possible) root cause. Either way I want to seal up the cracks as this is a fairly "wet" area of the boat and I want to keep water out of the transom and hull.

As context, I took the boat to the repair yard for a 25-ish-year overhaul - to catch up on some neglected maintenance (but not a "restoration" project). Overall the boat is in great shape, but a couple areas looked like they to needed some attention in order to extend the life of the boat. She's a beautfiful boat but I am not too concerned about cosmetic stuff. Rather I am prioritizing addressing all areas of potential water intrusion. If it is deemed to be necessary (or at least less-problematic), moving the lower holes isn't going to cost me too much extra at this point, as they are already in the midst of resealing and reinstalling all the brass drain tubes and will be doing some spot gel coat repairs to patch old deck holes where old batteries and tanks were once mounted. I am also having the old transducer removed and patched - in order to minimize the number of holes in the hull below the waterline.

If I keep the lower holes in their current location, what do you suggest for minimizing the chances of cracking the splashwell gel coat again? Do you think bent washers (per the dealer service bulletin) would be better than the rectangular aluminum brackets that are currently being used? Flymo - how are your lower bolts secured or reinforced at the splashwell?

Thanks again for comments and suggestions - I really appreciate it.
1992 Sport GLS 15

OregonWhaler
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Joined: Sun Sep 25, 2016 11:53 pm

Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby OregonWhaler » Tue Oct 18, 2016 1:33 pm

I am going to try to get back to the boat yard this week to take photos and some additional measurements.
1992 Sport GLS 15

OregonWhaler
Posts: 5
Joined: Sun Sep 25, 2016 11:53 pm

Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby OregonWhaler » Tue Oct 18, 2016 2:24 pm

For reference - here is a photo of the transom/splashwell of a 15' owned by 'wlagarde' from Whaler Central. It looks like the upper holes were drilled than mine, while the lower holes are maybe 1" higher than mine. He said he used the "green" hole spacing for the lower holes. I like the look of his lower bolts - as the bolts and washers comfortably avoid the splashwell radius. I emailed with him and he said the transom has remained solid mounting this way.

However, he does now have a jack plate : /


splashwell_wlagarde.jpg
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Mounting_Bolt_Pattern.jpg
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1992 Sport GLS 15

flymo
Posts: 189
Joined: Thu Oct 22, 2015 2:58 pm

Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby flymo » Tue Oct 18, 2016 2:28 pm

Anthony, regarding the 1" height, that was simply my guess based on your third pic, which showed the "hook" in the transom mount roughly 1" above the top of the transom. If mounted all the way down, it would be resting on or very close to the transom. Or so it looked from the picture, maybe I didn't see it right.

On my setup, because the lower holes are also very close to the radius in the splashwell, and I had some minor cracking from the previous motor install, I made two curved reinforcing plates out of 316 stainless steel and caulked them into place.

Here is the transom without the motor:

DSCN0554.jpg
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Making the plates and the finished product:

DSCN0555.jpg
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DSCN0559.jpg
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Last edited by flymo on Wed Oct 19, 2016 5:36 am, edited 2 times in total.

flymo
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Joined: Thu Oct 22, 2015 2:58 pm

Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby flymo » Tue Oct 18, 2016 5:46 pm

and then here are the plates installed, complete with spruce needles:

DSCN0652.jpg
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and with the motor ("two holes up" from the lowest mounting):

F70wsteering.jpg
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I do still have a chunk of the 316 tubing; you are welcome to the leftover if it will help with your situation. It was just hand work, with a hacksaw and hammer - seems like it might be just the ticket. I did not patch any of the gelcoat, just caulked the cracks and behind and around the plates. I am quite sure no water is getting in.

Unfortunately my boat is in another state, so I can't do any measuring right now, but I would recommend starting with your AV plate about an inch above the keel line (with the motor trimmed so the AV plate is parallel with the keel). Also, I can't say enough about how the right prop will affect your performance - do you have a tach installed?

Flymo
Last edited by flymo on Wed Oct 19, 2016 7:56 am, edited 4 times in total.

jimh
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Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby jimh » Tue Oct 18, 2016 7:39 pm

The location of the engine mounting holes as recommended by BIA is described in the FAQ. See

http://continuouswave.com/whaler/reference/FAQ/#Q9

I think Flymo may be correct: the location of the upper holes as seen on your boat transom look like they are closer to the transom than the normal spacing, which is 1-7/8-inch below the top of the transom.

I would not make a new lower-hole in the transom with a spacing from the upper holes of only 6-1/2-inches. If you were to do that, the engine would have to be mounted at least two-holes-up at a minimum. Since your mounting holes on your transom may already be elevated, you'd be stuck with the lowest possible engine mounting height of more than two-holes-up. That would be a mistake in my opinion.

Perhaps the initial installer altered the standard transom hole layout because of concern about the lower hole clearing the bottom of the splash well. The installer may have moved the entire set of holes higher than normal.

Flymo's special mounting brackets to reinforce the lower holes on the inboard side of the transom look like a good solution.

I used to own a 1976 SPORT 15. The lower mounting holes were drilled on an upward angle from the stern toward the splash well.

OregonWhaler
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Joined: Sun Sep 25, 2016 11:53 pm

Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby OregonWhaler » Tue Jul 18, 2017 6:38 pm

I thought I should post an update after finally getting our 15' Whaler back in the water a few times this season.

Per the chain above, at the end of last season, I was trying to determine if I should raise the engine height by 1.5" or 0.75" due to porpoising problems and an awkward spray pattern from the motor. Thank you to JimH and Flymo for sharing their opinions and expertise last year. It is much appreciated.

I ultimately decided to raise the engine by 0.75" and, after about 7 hours run time in a variety of river conditions over the last couple of weeks, I can report that I am extremely pleased with the results. I am yet to notice any negatives since raising the engine. Rather, it has been a huge improvement overall. The boat gets on plane much sooner and at a lower engine RPM.

The odd splash pattern has been eliminated and I can now cruise at a lower boat speed and engine RPM with the boat staying on-plane nicely. The boat also seems less sensitive to wakes or headwinds--with the bow staying planted thus far. I also now have some actual range in the trim to play with. Previously I had to keep the motor trimmed all the way in, otherwise it would immediately porpoise.

I am pleasantly surprised by just how much difference the 0.75" height increase has had on the handling characteristics of the boat. I think my wife thought I was nuts last year when I was endlessly pondering the pros and cons of 0.75 v. 1.5 inch, but even she immediately noticed improvements and appreciates the lower cruising speed required to stay on plane. It makes for a much quieter and more relaxing day on the boat.

Due to challenges with storing the boat (our garage renovation is still on hold - requiring us to pay for dry storage) we had very reluctantly been considering selling the boat. However, since getting it back out on the water we quickly put that on hold :-)

In other news, the local boat yard I worked with here in Portland did a fantastic job replacing all the brass thru-hull drains and remounting the engine (including patching the old holes). It looks as good as new!

I'll try to post some video links of the boat on the water soon.

Thanks again to jimh and flymo for their tech support!
1992 Sport GLS 15

jimh
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Re: Engine height: 1992 GLS 15 with 2002 Mercury 50 HP 4-stroke EFI

Postby jimh » Tue Aug 15, 2017 12:19 pm

I am glad you didn't sell the GLS 15.

The improvements in handling that resulted
mainly from the change in engine mounting height are very interesting and will be useful for many others to know. Thanks for the follow up post.