Forum: WHALER
  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Correcting Static Trim in Stern Heavy 13-footer

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Correcting Static Trim in Stern Heavy 13-footer
fishlips posted 11-10-2008 04:53 PM ET (US)   Profile for fishlips   Send Email to fishlips  
I recently re-powered my 13-footer to a 40-HP Mercury FOURSTROKE from the 40-HP Johnson two-cycle that came with it. I love the new motor and its power trim, and I have no problems with handling. However, [the 13-foot Boston Whaler boat is] very stern heavy at this point as the 40-HP Mercury FOURSTROKE weighs a whole lot. I think an Armstrong bracket with floatation would do [correct the stern-heavy problem], however I don't think they make anything for a boat this small. I understand [Armstrong brackets] are very pricey, anyway. It's too late now to go with a smaller motor. Does anyone have any other ideas?
pglein posted 11-10-2008 06:23 PM ET (US)     Profile for pglein  Send Email to pglein     
Move weight forward. Get a fuel tank that fits under the front seat. Move the entire seat system a little bit forward. Put a substantial chain and rode system in the bow locker to go with your anchor. If you have the newer trapezoidal anchor locker, put a heavy anchor in there.

This is the primary reason that I did not upgrade my 13' with a 4 stroke motor. They're simply way too heavy for that boat. I believe the motor you have is about 240#. A comparable 2 stroke would be about 180#.

BooBoo posted 11-10-2008 09:03 PM ET (US)     Profile for BooBoo  Send Email to BooBoo     
I agree with pglein. 40hp 4-strokes are too heavy for 1998 and earlier 13 hulls. Try the new 2009 Evinrude 25-30hp E-tec motors or go back to an older 25-40hp 2-stroke. Best in my opinion is 40hp 3-cylinder 40hp 2-stroke Yamaha.
Slick 50 posted 11-11-2008 09:31 AM ET (US)     Profile for Slick 50  Send Email to Slick 50     
I feel for you, spend money then unhappy. Wish I had a small engine to swap with you.
I have a 14'4" Wahoo with a 260# Yamaha 90HP 2 stroke. This engine is at the weight limit of the hull and 150% of rated HP.
Are you concerned with the boat sitting and being stern heavy or is it while under way?
I have added Smart tabs to the Wahoo with great results due to the stern heavy Wahoo. The tabs have improved porpoising, high speed control and low speed plane.
I also moved the battery to the console, it was in the stern. Have a healthy anchor with chain in the bow storage.
Floatation sponsons or brackets are a possible.
fishlips posted 11-11-2008 12:31 PM ET (US)     Profile for fishlips  Send Email to fishlips     
Thanks for the feedback folks. Yeah the original intent was to put a smaller motor on it. I was out of town and asked my Dad to handle dropping the boat off. Do you remember Tim Allen's Tool Time character? Patterned after my Dad, I'm sure. I'm lucky I didn't end up with a 70-HP now that I think about it :)

The boat handles very well underway so that's not a [concern], in fact I now have power trim so handling has [improved] considerably overall. The [concern] is that I'm so low in the stern I can't even tow the kids behind me in a tube anymore. The stern will take a dip when I try to take off. I also have to give it a little gun after if I come to a quick stop to keep water from splashing over the transom. I'm not going to sink, but these are not good things.

pglein I had the same thoughts on moving the weight forward and I hope that will do the trick. I have plans to move my batteries up front, adding a second battery for more weight up front, and who couldn't use a second battery on board. I already removed the 11-gallon under-bench tank I had mounted under the driver's bench. I was hoping to avoid moving everything, but I just don't think there is any other way.

Thanks again, and wish me luck!

elaelap posted 11-11-2008 01:11 PM ET (US)     Profile for elaelap  Send Email to elaelap     
You might want to check out this recent discussion about adding and adjusting weight to improve trim:
http://continuouswave.com/ubb/Forum1/HTML/016923.html
I think that it wouldn't take much weight at all way up forward to greatly improve the trim of your light boat. Remember that your 13 has many hundreds of pounds of positive floatation, and with a 40-HP motor on that little skiff, I don't think you'll notice any change at all in performance with the addition of a relatively modest amount of weight. Good luck.

Tony

Tohsgib posted 11-11-2008 01:22 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
I have the same weight on my transom. I have a 1994 Evinrude 40-HP that weighs about 182-lbs, a SS propeller so say 19-lbs, and then a CMC PT130 PTnT system that weighs another 45-lbs. Yeah she sits low when going slow with two in stern so I just move a person up front when going slow. Same would apply when towing a tube, you need a spotter anyway. I found 40-lbs of lead in front hatch does wonders.
stayinstrewn posted 11-11-2008 08:55 PM ET (US)     Profile for stayinstrewn  Send Email to stayinstrewn     
[I] have similar problems [with] my [13-foot Boston Whaler boat and a] Johnson 40-HP two-cycle motor. The quick fix: put somebody up forward! Sitting on the mooring or dock, the boat definitely sits low which puts the waterline underwater. We've looked into putting a gas tank under the forward seat, but that is well over $150. I like the idea of putting the battery under the side console and move the oil up, too, if there's room. That would help out substantially. In the interim, we now just keep both 6-gallon tanks up front. An [inconvenience], but not huge deal.

SS

Austin Whaler posted 11-18-2008 03:20 PM ET (US)     Profile for Austin Whaler  Send Email to Austin Whaler     
Get a rubber plug, put in the drain hole in the anchor locker, then fill with water that adds weight into the front. That is easy to get rid of, if you have somebody that is sitting up there.
BQUICK posted 11-18-2008 03:57 PM ET (US)     Profile for BQUICK  Send Email to BQUICK     
Who wants water splashing around? Not enough weight anyway. Put bags of lead shot in the forward locker.
Tohsgib posted 11-19-2008 01:23 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Water weighs 8-lbs a gallon, front locker holds less than 3 gallons. Lead weights are VERY heavy and hence why i use them, plus they don't grow algea.

I recently just swapped my two-cycle for a Johnson four-cycle which is a tad heavier than his Mercury FOURSTROKE. I will let you know my static trim findings when I splash it this week or this weekend.

For those who speculate that a 40-HP four-cycle is too heavy for a classic 13-foot Boston Whaler hull, you are incorrect. It just takes a bit of cleaver weight repositioning and, VIOLA, all is good. And still have 40-HP on the back. If we Americans as a whole would lose 20-lbs and stop eating junk food, these heavier engines would be close to a wash.

daveb posted 11-19-2008 08:16 PM ET (US)     Profile for daveb  Send Email to daveb     
Get the battery out of the stern and in front of your seat, monted on the opposite side. 40 pounds or so three feet further forward will help if you have not done it already

Dave

Jefecinco posted 11-20-2008 08:30 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Put about fifty pounds of diver weights in the forward locker. They won't take up much space. Adding a lot of chain and a heavier anchor will help but makes anchoring more difficult and is of no help when at anchor.

If the fifty pounds is not the ideal weight it is easy to add or remove one weight at a time to tune the balance to the perfect setting.

Enjoy the new engine and thank your Dad.

Butch

jimh posted 11-20-2008 09:28 AM ET (US)     Profile for jimh  Send Email to jimh     
To improve the static trim by adding an stern appendage for mounting the motor (also called a buoyancy box) is an approach that Boston Whaler used in their Whaler Drive models. Buoyancy is proportional to the water displaced. Water has a density of about 1-kilogram per liter, or about 62-lbs per cubic foot.

The specified draft of a 13-foot Boston Whaler boat is 6-inches and its beam is about 5-feet. A buoyancy box that was almost full width of the boat, one foot long, and immersed 6-inches, would displace 5 x 1 x 0.5 = 2.5-cubic-feet of water, providing about 2.5 x 62 = 155-lbs of buoyant force.

This buoyant force of 155-lbs would have to support:

--the added weight of the new, heavier motor
--the added weight of the buoyancy box itself

Exactly how the trim would be affected would be influenced by the added length of the moment of the engine weight and how the hull's center of pitching resistance moved forward.

You'd also have to be concerned about how the buoyancy box was attached to the transom, as there would be considerably more stress on the transom when the boat was out of the water. When out of the water all the buoyant force disappears, and the stern appendage and original transom have to be strong enough to bear all of the added weight and greater bending moment.

jimh posted 11-20-2008 09:31 AM ET (US)     Profile for jimh  Send Email to jimh     
Whether or not there is "floatation" inside the stern appendage does not change how it creates its buoyant force. Building a stern appendage with just air in it would be the most buoyant, as any material used as a filler will just add weight and no buoyancy.

Foam filling adds no buoyancy. It just keeps water from occupying that space in the event of a hull breach. Buoyancy comes from the hull form and how much water it displaces.

Tohsgib posted 11-20-2008 11:49 AM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Hence why steel and ferro-cement boats float. Keep the water out and all is good.

When I ran a lighter 2 stroke I would carry 12 gallons of gas in 2 6 gal tanks. These tanks weigh about 55lbs each when full. Now with my new technolgy outboard I can run the same with 1 6 gallon tank and therefore make the extra weight a wash. This also frees up much valuable storage space and I get rid of the VRO tank which is probably another 15lbs or so full.

towboater posted 11-20-2008 03:17 PM ET (US)     Profile for towboater  Send Email to towboater     
Toshgib.

Curious if you think a 6" setback bracket (25 lb ish) AND moving gas/batts/lead fwd would help?

pglein posted 11-20-2008 05:08 PM ET (US)     Profile for pglein  Send Email to pglein     
A setback bracket would only move that weight farther aft.
towboater posted 11-21-2008 12:53 AM ET (US)     Profile for towboater  Send Email to towboater     
Yeah, a setback would move the weight further aft, but, wouldnt the same weight you plan to move fwd level out the trim better?

Nahh, 6" and the added weight of the setback itself isnt worth the trouble.

Tohsgib posted 11-21-2008 10:47 AM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
I mounted mine on the transom. I might go with a jackplate considering I swear by them but at 243lbs, I don't want to offset that even more.
towboater posted 11-21-2008 11:20 PM ET (US)     Profile for towboater  Send Email to towboater     
My questions about using a jack plate assumes the heavier engine is using the same mounting holes as the prior engine...and thus the stern is heavier, the prop is lower, and thus tilting the eng this way or that will not help. Would a jack plate allow fishlips mount the same transom holes yet lift the engine as high as possible and trim it out or in for better performance?

Tohsgib posted 11-24-2008 11:02 AM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
The jackplate uses existing transom holes. You then bolt the engine to the plate. The plate allows for 5-6" of verticle lift from stock height. I find that 4- 4.5" is usually about the max and it still performs almost stock as far as turning and running in following seas but now draws less water and picks up a few hundred rpm which in turn gives a couple/few more mph.

Post New Topic  Post Reply
Hop to:


Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.