Notices
The Boating Forum

Outboards on Bertram 46

Old 04-11-2020, 04:36 AM
  #1  
Junior Member
Thread Starter
 
Join Date: Apr 2020
Posts: 4
Likes: 0
Received 1 Like on 1 Post
Default Outboards on Bertram 46

I am considering guttering out the salon of my Bertram 46 leaving the galley and 2 rooms below and taking off the fly bridge and putting on a light weight tower. This will significantly reduce the weight of the boat and now install outboard motors. I would be happy with 25knot cruise. Anyone knows of a similar project and the results? Please share comments on this project.

Popular Reply

04-11-2020, 09:04 AM
bills106
Senior Member
THT sponsor
 
Join Date: Aug 2011
Location: Beaufort NC
Posts: 6,152
Received 2,798 Likes on 1,303 Posts
Default

I'm trying hard but I can't come up with a worse candidate for an outboard conversion project. Way, way to heavy and the near-constant deadrise hull shape was tough enough to push for the 12V71's that a lot of the later ones came with, the earlier ones with 8V71's would only plow and never really plane out.

They were renowned for bulldozing through any conditions short of a cat 5 hurricane and while they'll roll the lard out of a biscuit, they will keep going and defined the legendary Bertram toughness. A nice new shiny pair of C-18's would likely be a less expensive addition and really increase her performance and market value.
Old 04-11-2020, 04:50 AM
  #2  
Senior MemberCaptains Club Member
 
Join Date: Mar 2003
Location: Annapolis MD USA
Posts: 989
Received 227 Likes on 155 Posts
Default

Guy on here did a nice job with a 28 and now is stretching another Bert user id DayTrip. That is a lot of boat to move with outboards. I have seen a few 31's done never a 46 would guess you are going to need at least 3-4 big egg beaters to get anywhere near 25kt. They won't last very long but it is your money.
B

Last edited by brisboats; 04-12-2020 at 12:02 PM.
Old 04-11-2020, 04:58 AM
  #3  
Admirals Club Admiral's Club Member
 
Join Date: Dec 2016
Location: Apollo Beach, FL
Posts: 1,396
Received 728 Likes on 324 Posts
Default

I would think quads minimum no matter the OB. But there are several big block outboard choices today that will be up to the task.

Welcome to THT, a bunch of old grumpy guys are gonna come in here and call you names for thinking about doing this but trust me, plenty more of us want you to ignore them and do it. There are guys here that act like you just punched their wife if you talk about converting a diesel seavee to outboards.

if you do this project please start a build thread here and document it, would be awesome to see!
Old 04-11-2020, 05:05 AM
  #4  
Senior MemberCaptains Club Member
 
Join Date: Dec 2004
Location: Lower Bay in VA.
Posts: 6,019
Received 289 Likes on 162 Posts
Default

Maybe with 4 Seven-marine outboards . Ready to spend 400k on a repower ?
Likes:
Old 04-11-2020, 06:14 AM
  #5  
Admirals Club Admiral's Club Member
 
Join Date: Apr 2006
Location: New England
Posts: 3,912
Received 941 Likes on 586 Posts
Default

Are you super handy? Do you have lots of experience working with fiberglass?

Sounds to me that you would end up spending a ton of money two years time and end up with an old hull that is a total one off you may love but only worth about 1/3 of what you have into it.

I usually say to people consider selling and moving on.
Old 04-11-2020, 06:21 AM
  #6  
Senior Member
 
Join Date: Aug 2016
Posts: 1,497
Received 419 Likes on 286 Posts
Default

You Wont! lol I think there will be a lot of conversions of this nature in the future but a 46' is ambitious! looking forward to design drawings best of luck
Old 04-11-2020, 06:28 AM
  #7  
Admirals Club Admiral's Club Member
 
Join Date: Jan 2017
Posts: 1,342
Received 390 Likes on 233 Posts
Default

What do you think it weighs without current power?
Old 04-11-2020, 06:40 AM
  #8  
Admirals Club Admiral's Club Member
 
Join Date: Apr 2009
Posts: 1,285
Received 200 Likes on 127 Posts
Default

A 46 Bertram is far different than a large CC. Hull design, beam width, displacement and weight distribution. You are talking probably quad 425’s to move it with any speed. You are talking a high priced bracket plus a ton of fiberglass and stringer work. You are most likely talking more cost to do what you want to do than a inboard diesel repower.

If you want more speed and new motors put in a pair of QSM11’s. If you just want more space go look at a 96 or newer 48 Ocean. You can buy one with cats for $200k and have a great boat.

I would say an outboard conversion would cost $150 to $200k on that boat to be done right.
Likes:
Old 04-11-2020, 06:41 AM
  #9  
Admirals Club Admiral's Club Member
 
fireisland1's Avatar
 
Join Date: Jun 2011
Posts: 5,832
Received 3,131 Likes on 1,379 Posts
Default

I don’t think it’s crazy. I’m just not sure what you will achieve. 120k or more for power, year worth of work and scratching. Maybe another $50k for refitting. and offer all that you are not sure of weight/balance.
Likes:
Old 04-11-2020, 06:46 AM
  #10  
Admirals Club Admiral's Club Member
 
Join Date: Dec 2009
Location: Lake Jackson, texas
Posts: 629
Received 279 Likes on 161 Posts
Default

It takes a lot of power to push a 46 Bertram. I would be more concerned about the deadrise than the weight and beam. If you do it at least you can move the generator into the engine room and out of the lazarette.
Old 04-11-2020, 06:47 AM
  #11  
Senior Member
 
Join Date: Jun 2006
Location: Lower Potomac, VA
Posts: 3,359
Received 379 Likes on 254 Posts
Default

As said above, 4 Marine Seven$ would probably get the job done, but something that hasn't been mentioned, but needs to be....balanced weight. You're taking out a couple big ass engines that are a good 10' from the stern and replacing with 4 heavy engines and a bracket hanging off the transom. You will also need to beef up your transom big time to handle all that weight and power torque. You have completely changed the balance of all that weight. Could be a real problem.

Hate to say it, but this is a bad idea which will cost a ton of money, lots of time and will greatly devalue your boat.
Old 04-11-2020, 07:22 AM
  #12  
Admirals Club Admiral's Club Member
 
fireisland1's Avatar
 
Join Date: Jun 2011
Posts: 5,832
Received 3,131 Likes on 1,379 Posts
Default

Pushing a boat from the stern is way different then pushing it from midship stringers.
Old 04-11-2020, 07:49 AM
  #13  
Admirals Club Admiral's Club Member
 
Join Date: Jan 2008
Location: S. Florida
Posts: 6,321
Received 1,646 Likes on 855 Posts
Default

Outboards are going to have a bigger spread between cruise and top speed. A 24knot cruise with diesels maybe wants a 30-32knot top speed, but you’re going to want a top end closer to 35-38 knots to have the right power. You can do it with less, but it will feel like a pig even if it “works.” Check out a 33 Grady with twin 225s for an example. It worked, and it cruised mid-20s, but it felt like a pig getting on plane and there’s no comparison between the way cruise speed feels in a big sea between wound up gassers and diesels solidly in their power band.

I think the posters above are exaggerating what that will take, but it will take a lot. Twin Yamaha 425s would maybe leave you with a boat that performs like the 33 Grady with 225s... if you’re right and you manage to take a bunch of weight out of the hull. I’m guessing it’ll take you trip 425s to get a mid-20s cruise.

how long will the shafts have to be to get clean water on that deep vee? How much will you need to change to re-balance the boat?

I’m all for seeing you do the project, but I’d be sure you get professional help because you will spend a lot of money and it will be really easy to have an expensive disaster.
Old 04-11-2020, 08:01 AM
  #14  
Senior Member
 
Join Date: Jun 2014
Location: Middle Sound, NC
Posts: 8,884
Received 1,690 Likes on 1,087 Posts
Default

Mid engine(s) will be swamped to reach clean water below transom. Transoms on these are pretty deep in the water, especially shifting CG back.
Old 04-11-2020, 08:16 AM
  #15  
Senior Member
 
Join Date: Feb 2010
Location: Palm Beach Gardens FL
Posts: 1,685
Received 379 Likes on 208 Posts
Default

Originally Posted by Corndog38 View Post
Mid engine(s) will be swamped to reach clean water below transom. Transoms on these are pretty deep in the water, especially shifting CG back.
The mid engine depth will indeed be an issue. Another issue might turn out to be prop diameter. A 46 Bert swings some pretty big wheels because it's a big, heavy deep vee. It takes diameter and torque to get that boat up and going.
Old 04-11-2020, 08:18 AM
  #16  
Senior Member
 
Join Date: Sep 2009
Location: Maine
Posts: 1,004
Received 71 Likes on 40 Posts
Default

Would be curious to hear people’s take on concern over potentially submerging the outboard (farthest port and starboard) engines when that big girl rolls a bit to one side with a fairly short period slop from the stern.
Old 04-11-2020, 08:41 AM
  #17  
Senior MemberCaptains Club Member
 
Join Date: Feb 2009
Location: Sarasota, FL
Posts: 3,187
Received 353 Likes on 186 Posts
Default

I would pick up four Yamaha 350s, have all of them torn down and rebuilt by the best tech you can find. Build them with the same care as you would a race engine including the lower units. Send the ECU's to Nizpro and you'd have quad 425's for 1/3 the price. The other benefit of the 350's is Latham makes extension kits to make them a 35" or even 40" shafts for your center motors. Not sure these kits are available for the new 425s? I'd also keep the tower and glass parts to a minimum not only on weight but size. Wind drag is a bitch.
Old 04-11-2020, 09:04 AM
  #18  
Senior Member
THT sponsor
 
Join Date: Aug 2011
Location: Beaufort NC
Posts: 6,152
Received 2,798 Likes on 1,303 Posts
Default

I'm trying hard but I can't come up with a worse candidate for an outboard conversion project. Way, way to heavy and the near-constant deadrise hull shape was tough enough to push for the 12V71's that a lot of the later ones came with, the earlier ones with 8V71's would only plow and never really plane out.

They were renowned for bulldozing through any conditions short of a cat 5 hurricane and while they'll roll the lard out of a biscuit, they will keep going and defined the legendary Bertram toughness. A nice new shiny pair of C-18's would likely be a less expensive addition and really increase her performance and market value.
Likes:
71Outrage, Burgmane, efx, Gunner38, HighInterest, old hat, prowlersfish, RLC2020, starbright55, WavRidr359, Windwood and 6 others liked this post. (Show less...)
Old 04-11-2020, 10:17 AM
  #19  
Senior Member
 
Join Date: Mar 2010
Location: Austin
Posts: 1,799
Received 258 Likes on 208 Posts
Default

I would think the engines would be mounted so low that they would be underwater at all but planing speed. Then any overtaking waves would submerge them again.
Then there is the little bitty propeller problem.
Old 04-11-2020, 11:04 AM
  #20  
Senior Member
 
Join Date: Oct 2014
Location: N.E. CT
Posts: 3,970
Received 1,707 Likes on 851 Posts
Default

I’ll hold my thoughts, but just say the place to start a project like this would be with an experienced well qualified N/A.

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.