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Pro-Line 251 getting some love...I/O to Suzuki O/B

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Pro-Line 251 getting some love...I/O to Suzuki O/B

Old 02-20-2017, 04:13 PM
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Default Pro-Line 251 getting some love...I/O to Suzuki O/B

I've been contemplating this conversion for quite some time. Over the last couple of weeks I have committed to this project, with the intent to do most of the work myself......I am a fairly competent backyard mechanic; have maintained the engine and drive with routine maintenance, fixed electrical things, installed my electronics, etc. But, never taken on a boat project of this size........admittedly, much less work than many of the re-fits detailed on THT.

I am the original owner of this 1998 251 Pro-Line. It has 3843 hours of running time on 2 different engines and outdrives. I decided on I/O originally because the outboard option at the time was Honda 130 or 225hp smoking 2-strokes. A 300hp Volvo Penta package was a better combination of cost, reliability, and economy IMO. The boat has been lift stored which has unquestionably helped the outdrive's longevity and reliability.

I decided a few months back that if I could sell the VP package as a running take-out, then I would convert it to bracketed outboard. This model was sold in either configuration, with bracketed twin 2strokes as an option to 300hp. So, the whole weight and balance question is not too much of a player here. My power choice will be a single Suzuki 300.

So, why not just sell it and buyer newer??? Fact is, I still really like the boat.

It is economical on gas, has terrific range with a 170 gallon tank, good storage below the helm seats, 2 big macerated fishboxes, planes in the mid-teens, is easily fished when solo, has the overnighter package with stove, frig, and macerated head. Most importantly, it is a wood free hull. I won't to get into any rot issues.

Last week I stripped out the Volvo package and sold it

In addition, I am planning other upgrades that I have desired for a long time...
1) Electronics upgrade to include an auto-pilot. The cost and inaccessibility of an autopilot for an I/O had always prevented it.
2) A functional bait tank. The installed one is useless. It is centered in the transom, shallow and narrow, and sloshes horribly when on the drift. Currently, my plan is too fabricate a deeper tank of about 25 gallons and place it in the transom where the sink is (port side).
3) Cut out the bait tank. This will free up a lot of depth in the transom (above the I/O hole). My idea is to install a custom tackle storage unit into that space.
4) Upgrade the helm with new Blue Seas fuse boxes and Contura panels.

One of the more interesting discoveries so far....The stringers at the forward motor mounts are hollow.

I am curious to know if all 251's are like this or if this was specifically done for the I/O option?;?;?;? The stringer is foam filled both forward and at the transom.
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Last edited by a7ewizard; 07-28-2017 at 05:20 PM. Reason: replace pics
Old 03-11-2017, 08:52 AM
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Default Pourable expanding foam to fill outdrive cut??

First of all, Kudos to Pro-Line for using divinycell core in this transom. There is no damage or delamination to repair other than the hole itself. Of course, no rot either. There is a bit of warpage to the exterior transom due to the weight of the drive hanging on it for the past 18 years. More work to prepare for the bracket....

However, in cutting the hole for the drive, someone really hacked away at it. There is no way to cut a plug that will fit nicely without large voids to fill. Additionally, divinycell or Coosa is hard to find in my area or pricey to ship. I don't want to introduce wood into the transom; so a plywood plug is not an option. Enlarging the cut to allow for a better fitting plug seems like a way to weaken the transom.....

This is my idea. I've purchased some 4# expanding foam that I will be using to fill my hollow stringer sections. What if I bolt pieces of plywood to both sides of the transom, using the existing transom assembly bolt holes. I'll line this plywood with plastic backed heavy freezer paper to allow their removal. Through a small hole on the inside piece of plywood simply pour in the expanding foam. This should give me a near perfect fill of the transom hole that I can glass over to complete the repair.
Old 03-22-2017, 06:15 PM
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When I pulled the forward engine brackets off the stringer, water gushed out of the bolt holes. I suspect that during periods of rain and wash downs, water seeped past the I/O engine cover, then dripped onto the stringers and past plastic plates placed above the stringer access cutouts. As the forward stringer sections are foam filled, it has taken a long time for water to seep aft and for the stringers to dry out sufficiently. Today, I had a chance to pour some 4# foam into each stringer. I used about 2/3 of a gallon each of Part A and Part B.

While waiting to do this pour, I stripped the bilge and prepped for fiberglass work. My plan is to reinforce the transom and some of the joints in preparation for the outboard bracket:

I decided to purchase a bracket from Stainless Marine. They were the OEM supplier to Pro-line back in the day. Jerry has been with SM for many years and is a wealth of knowledge and very helpful in assisting me with this. I sent him photos of my boat, measurements, stringer spacing, etc. It has to be correct the first time since it is being shipped to California!
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Old 03-22-2017, 06:22 PM
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Thanks for posting I'm keeping an eye on this build, one day I'd like to convert a 25 or 26 from io to ob.
Old 03-22-2017, 06:31 PM
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Gonna watch as well. I have a 99' 25'1" WA. Has single 225 Optimax that runs like a champ.
Old 03-22-2017, 06:55 PM
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Originally Posted by KGonzalez23 View Post
Gonna watch as well. I have a 99' 25'1" WA. Has single 225 Optimax that runs like a champ.
It only took 3 posts to find some people interested LOL.

KGonzalez would you mind posting some pictures of your 251, detailing the bilge layout with pumps etc and the access hatches to the bilge and transom? I'd like to see how PL did it originally.

I may just cut down the top of the I/O box to make the hatch cover. Glass in the aft floor at the transom cut out and glass about 12 inches up. I could build up a 2 inch ridge around the cockpit hole to keep water from entering the bilge. Problem will be the hatch cover will be maybe 3-4 inches higher than the cockpit deck. Easiest solution though.

The transom hole will probably get fitted with a custom tackle center...
Old 03-22-2017, 09:09 PM
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Sure will.

Can you tell me how to post photos in the body of a message and not as a link
Old 03-22-2017, 09:35 PM
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Shit, you're a real man. This is a great damn project & I commend you for taking it on.

Q: Do you feel the 4# foam is structurally sound enough to augment the stringers?

I was thinking a mash-up of epoxy resin with fiber filler (powder) would make a rock-solid stringer that'd never ever take on water. I suspect your route will work as well- or better than- the original.

What prompted you to do a single 300, rather than a pair of 150 or 200 OB's? I'm not criticizing, just wondering what your line of thought was.

BTW: Looks like you're doing an excellent job so far. Please keep us updated. Awesome project.
Old 03-23-2017, 08:30 AM
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Originally Posted by KGonzalez23 View Post
Sure will.

Can you tell me how to post photos in the body of a message and not as a link
I use Photobucket to host photos. Upload the pic to your account, click on the IMG link (turns blue), right click to copy, then paste into the body of your forum post.
Old 03-23-2017, 08:45 AM
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Originally Posted by TipDS View Post
Shit, you're a real man. This is a great damn project & I commend you for taking it on.

Q: Do you feel the 4# foam is structurally sound enough to augment the stringers?

I was thinking a mash-up of epoxy resin with fiber filler (powder) would make a rock-solid stringer that'd never ever take on water. I suspect your route will work as well- or better than- the original.

What prompted you to do a single 300, rather than a pair of 150 or 200 OB's? I'm not criticizing, just wondering what your line of thought was.

BTW: Looks like you're doing an excellent job so far. Please keep us updated. Awesome project.
I learned that 4# is most commonly used and is the minimum weight foam approved by Coast Guard for flotation requirements. Using epoxy would cost a fortune. Each void was over a gallon of volume. Just seemed to be the proper thing to foam them while I had a chance.

I had a crack at the base of one engine support. The backing plate was not attached but laying inside the stringer. I believe this was the result of a local shop re-aligning the engine soon after I bought the boat. It does have 3800 hours of running time and this is the only issue I have discovered.


Since I needed to repair this and cover the cutouts in the stringers, I decided to add fiberglass to the stringer/hull joint and at the transom.

I did consider twin 140s and twin 150s. One of the tests I saw on the 140's seemed to indicate they might not have enough torque for this application and slower to plane. The heavier 150s weigh about 1000 pounds; that concerned me too. Twins are also more expensive and the bracket costs more also. My other PL has a Suzuki DF225 that has been great to own. Not about to go 2-stroke either. Cheaper to maintain a single too.
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Old 03-23-2017, 08:54 AM
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I thought of doing the same thing to my 26' Skipjack 262 but the $25000 cost put me off so I just put in a new 6.2 chevy crate engine for $5000
Old 03-23-2017, 08:56 AM
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Default Holy cow!

3,800 hours? On the original engine?

I love the Prolines. I've owned three and looking at number four for a repower.
Old 03-23-2017, 09:08 AM
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Originally Posted by 805gregg View Post
I thought of doing the same thing to my 26' Skipjack 262 but the $25000 cost put me off so I just put in a new 6.2 chevy crate engine for $5000
When I sold my Volvo Penta package, we discovered water in the outdrive during the Buyer's test run and inspection. That was indicative of my recent experiences....new raw water pump, exhaust manifold sensors, steering actuator, corroded fuel pump connector, manifolds and risers coming due. It was getting tired and I was tired of fixing things and I questioned its reliability.

The estimate I received for a complete, new VP 5.3 package was outrageous! Thus, I am on this path. Allows me to make some other modifications as well.
Old 03-23-2017, 09:18 AM
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Originally Posted by shoeman View Post
3,800 hours? On the original engine?

I love the Prolines. I've owned three and looking at number four for a repower.
No, second engine and drive (2300 and 2100 hours approximately). Original 7.4 Gi broke hard at 1475 hours. Swapped in a 5.7GXi which was a better choice; more room to work and better fuel economy and lighter. The original outdrive was swapped out shortly after; pitted upper and lower gear sets with burnt fluid. Never water intrusion. I believe it was from the high torque of the 7.4. Of course, VP didn't even offer an explanation or suggestion to improve longevity. To summarize their reply..."your out of warranty, tough luck".
Old 03-23-2017, 09:38 AM
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OP great boat, great vision and great work so far. I am a Proline fan and owner ('96 240) myself and an admirer of the 251 hull. I'll try to offer a bit of helpful (maybe) advice -

I have no idea if the transom layup was the same for I/O vs OB hulls, likely as not it was but you are in a good position now to hedge your bet with some reinforcement. A couple of "knees" tying the transom to the stringers can offer a whole bunch of solid for a minimum investment of time, energy and money. Doubled 3/4" marine ply coated with epoxy and some 12 oz biax are all you need. Literally 3 - 4 hours tops to fabricate and install and < $100.

I would also encourage adding a layer (or two) of tabbing with 3" biax tape anywhere you can reasonably reach - transom to hull sides and bottom and stringers to transom and hull bottom. Minimal expense for this but you will have to write a check in elbow grease.

Best of luck to you sir, when she's finished you should realize a nice increase in performance and economy, and no mas dog house
Old 04-01-2017, 09:59 AM
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I haven't done fiberglass work on this scale before. There is a learning curve to it. Reading about it and watching videos helps. First thing I can tell you is, the smoother the base the better the new glass will lay in. I used a 4 1/2 inch high speed grinder to prep most of the surface followed by a palm sander. This left slight gouges which proved hard to roll the air and excess resin out of. Often pressing hard with the brush itself worked better to squeegee the air out. I had to grind out some air spots and soft spots after the first layer but I am happy with the results.

Any way I worked on the inside first to gain experience so the outer transom should proceed better.

I sanded away the coating to have a better look at the transom interior. Its 2 inches thick. Layup is thinner on the interior.

To close up the transom, I decided to use 4# pourable foam. I bolted plywood to both sides. Plywood was lined with parchment paper for removal of the plywood after the pour.

Capped the hole to force the foam to expand up and not out the hole

I used 8 oz and it work almost perfectly


The little void at the top gave me issues in the first layer of glassing. I should have either filled it or ground it flat. I thought the resin would plug it and/or abit of extra matting would fix it. Not the case! Live and learn..

Ready to start the glass work

Light mat and some cloth to seal up the stringers

2 layers of heavy mat and 2 layers of 1708 to beef up the transom. A few layers of tabbing in the corners also. I also added a layer of tape where the through bolts for the new bracket will go

Painted on 1 layer of gel coat late yesterday. All this just took 16 ounces. Seems I underestimated the amount of resin needed and bought too much gel coat.
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Old 04-10-2017, 11:25 AM
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I've got a '97 251 WA with a sterndrive and a Merc block that has been a maintenance pain - following eagerly. It's a great boat but I'd love to do this conversion too.
Old 04-10-2017, 11:51 AM
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I have a 2003 20' Proline Walkaround "Walk20" hardtop that I love w/ a 150hp Yamaha fourstroke. Wishing you luck on your project.

Can you post so wide pics of your boat? I'd like to see what it looks like. before after etc.

sub'd.
Old 04-10-2017, 01:31 PM
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I'm worried about that core being sufficient to hang a motor. The I/O was transferring force directly to the stringers. Now, the bracket will be hanging on the transom and, when underway, the motor will be pushing by means of the transom, not the stringers. That foam core does not look like the kind of high density, high strength coring you would see in an outboard transom.

Maybe I am wrong and someone will chime in that recognizes that material, but I would at least verify before you go any further. Even adding glass, if the core material is not up to the loads between the layers of glass, you will eventually get a failure, possibly a catastrophic one. Between running hard, docking, turning at speed, reversing, and trailering, who knows how many different ways that core will be stressed between the two main glass layers. It's got to be an appropriate material to do it's work.
Old 04-10-2017, 01:45 PM
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Proline transoms are divinicell, a far cry from 4 lb foam which is better suited to a coffin box or cooler. The bigger sin I see is not tapering/feathering back the glass to allow adequate tie in to the original layup.

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