This is an appeal from a judgment n. o. v. granted in favor of a manufacturer and a seller in a products liability case. Although we see significant merit in plaintiff-appellants’ arguments,' appellants’ complete failure to advance below the theory on which the arguments are based forces us to affirm.
Following a judgment overturning plaintiff’s jury verdict, we review the evidence in the light most favorable to the plaintiff, Continental Ore Co. v. Union Carbide & Carbon Corp., 370 U.S. 690, 696 n. 6, 82 S.Ct. 1404, 8 L.Ed.2d 777 (1962). Appellants Theresa McPhail and her two minor children brought this action after her son, Timothy, was electrocuted in a sailing accident on the coast of the island of Culebra. Timothy was sailing a 16 foot Hobie Cat1 belonging to a friend, who was a passenger on the boat. Timothy sailed the Hobie Cat to a dock located in a small inlet to offer a sailing lesson to the owner of the dock. When the lesson was declined, Timothy pulled away from the dock and was blown further inshore while trying to tack out of the inlet. Not far from the dock, and approximately 50 feet from the inshore end of the inlet, the mast of the Hobie Cat came in contact with a high tension wire that hung only 20 feet over the water. Timothy was killed. The passenger was thrown clear and was not injured.
Theresa McPhail sued both the authorities responsible for the power lines and the manufacturer and seller of the Hobie Cat. Evidence was introduced at trial showing that the design of the Hobie Cat put the person sailing the boat in extreme danger of electrocution should the boat come near a power line. The aluminum mast is mounted in a metal frame that sits on top of two fiberglass pontoons. The mariner sits on the metal frame, holding a metal tiller arm that descends into the water. Because the fiberglass pontoons are effective insulators, the only way for current entering the mast to reach ground is to pass through the helmsman who has to be in contact with both the frame and the tiller arm. The owner’s manual contained a warning to avoid power lines when launching, indicating the manufacturer’s awareness of the danger.
Plaintiff’s expert testified at trial that a wire grounding the frame to the tiller arm would cost, at most, $10. The expert testified further that the wire would conduct most of the current entering the mast and would have saved Timothy’s life. Defendants’ expert contradicted this testimony, but the jury rejected defendants’ position, finding for plaintiffs against the seller and manufacturer.2
Although it is a close question, the facts set out above might make out a case of defective design under applicable Puerto Rican law, based on the theory of foreseeable misuse or accident and failure to provide readily available and economically feasible safety measures. See Mendoza v. Cervezeria Corona, 97 P.R.R. 487 (1969); Ferrer v. General Motors Corp., 110 P.R.R. 244 (1971). Puerto Rico adopted the California definition of manufacturer’s strict liability in tort in Ferrer and Mendoza. See Greenman v. Yuba Power Products, Inc., 59 Cal.2d 57, 27 Cal.Rptr. 697, 377 P.2d 897 (Cal.1962). Subsequent to the trial in this case, the Puerto Rico Supreme Court made clear that defects of design are included *606under the Puerto Rican definition of “defect”, and that the Restatement requirement that the product be “unreasonably dangerous”3 need not be met in order to impose liability. See Montero Saldana v. American Motors Corp., Puerto Rico Bar Ass’n Ref.No.1978-52 (May 31, 1978); Cronin v. J. B. E. Olson Corp., 8 Cal.3d 12, 104 Cal.Rptr. 443, 501 P.2d 1153 (1972). Moreover, Puerto Rico has adopted the rule announced in Daly v. General Motors Corp., 20 Cal.3d 725, 144 Cal.Rptr. 380, 575 P.2d 1162 (1978), that an injured victim’s assumption of the risk or contributory negligence will not bar but will only reduce recovery in a strict liability case. Montero Saldana v. American Motors Corp., supra. Thus, even if Timothy was negligent in sailing near power lines and that negligence contributed to the injury, his survivors would be entitled to some recovery.
Appellants make all of the foregoing arguments before this court. Unfortunately, the record does not reveal that one shred of this theory was presented to the trial court. Rather, the district court’s opinion granting judgment n. o. v. begins with the proposition that “Plaintiffs correctly rely upon the Restatement (Second) of Torts, section 388 . ”4 After quoting the supposedly applicable section, the trial court went on to hold that: (1) the possibility of electrocution from sailing into a power line is a known and obvious danger; (2) sailing into power lines is not a use for which a sailboat is supplied; (3) even if a shock from contact with overhead wires was a foreseeable danger, the suggested safety feature (a wire grounding the mast to the tiller) would actually increase danger because most power line accidents will occur while the boat is out of the water (on a trailer) and the user is in contact with either the frame or the tiller; (4) the warning in the owner’s manual was adequate; (5) posting all of the appropriate warnings on the mast would take up so much space as to be both impractical and unreadable; (6) there was no evidence that the Hobie Cat was in any way defective or dangerous; and (7) that any failure to warn was not the proximate cause of the injury — Timothy’s failure to see the power line was.
As an initial matter, our review of the trial record convinces us that many of the foregoing conclusions represent the trial court’s rejection of jury resolutions of conflicting evidence (e. g., the findings numbered 4 and 6 above) and findings based on no evidence in the trial record (e. g., the findings numbered 3 and 5 above). We doubt the propriety of the former and must reject the latter.
Nevertheless, we think that the judgment n. o. v. was correct as a matter of law under the rules set out in section 388 of the Restatement of Torts. Under that section, in order to incur liability a supplier must know that a chattel is unreasonably dangerous and fail to exercise reasonable care in warning of that danger. Restatement (Second) of Torts § 388, Comment a. In contrast to the general rule of liability without fault in products liability law, the rule of section 388 thus predicates liability upon a standard akin to common negligence. Applying this rule, we agree with the trial court that there was no duty to warn of the danger involved in sailing into power lines or, in the alternative, that “reasonable care” was exercised by warning of *607the obvious in the owner’s manual. “It is not necessary for the supplier to inform those for whose use the chattel is supplied of a condition which a mere casual looking over will disclose . . . Restatement (Second) of Torts § 388, Comment k. As the trial court put it, the danger involved in sailing a boat with an aluminum mast into a power line was “patent and obvious”.
As noted above, Puerto Rico does not apply a negligence or quasi-negligence standard of “unreasonably dangerous” conditions or “reasonable care” in warning to products liability cases. Mendoza v. Cervecería Corona, supra. Moreover, even in jurisdictions applying the Restatement rules of products liability, section 388 would not govern this case. The preamble to section 388 expressly states that section 402A provides the special rule governing commercial manufacturers’ liability.5 Restatement (Second) of Torts ’§ 388, at 300 (1965). In short, the judgment n. o. v. was a right decision under the wrong law.
Plaintiffs-appellants must bear the responsibility for this problem. The opinion granting judgment n. o. v. indicates that plaintiffs requested that section 388 be applied. The record does not reveal that plaintiffs argued any other law or theory to the trial court. Indeed, the pleadings, the plaintiffs’ pre-trial memorandum, the court’s pre-trial order, and plaintiffs’ memorandum in opposition to judgment n. o. v. all indicate that plaintiffs were proceeding on a theory that appellees were somehow negligent.6 Nor have appellants presented us with any argument tending to reconcile the law presented below with the more liberal view espoused by the Puerto Rico Supreme Court. Finally, the record does not reveal that any law other than section 388 was charged to the jury.7 Thus, we are not presented with a case in which a plausible, if avante-garde, theory of defective design was presented to a jury and later rejected in a judgment n. o. v. Rather, the only conclusion we can draw from the record, is that appellants presented section 388 to the judge, it was charged to the jury, and the judge correctly rejected a verdict that was incorrect as a matter of law. The fault and the consequences for presenting the wrong law below rest squarely on appellants, and we must affirm. See Herman v. Hess Oil Virgin Islands Corp., 524 F.2d 767, 772 n. 15 (3d Cir. 1975) (affirmatively leading trial court into error precludes appellate review); Reed v. AMF Western Tool, Inc., 431 F.2d 345, 349 n. 2 (9th Cir. 1970) (failure to include legal theory argued at directed verdict motion in subsequent requested instructions precludes appellate review when theory involves factual issues.
A party may not “sandbag” his case by presenting one theory to the trial court and then arguing for another on appeal. United States v. Gonzalez Vargas, 585 F.2d 546 (1st Cir. 1978). When plaintiff obtains a jury verdict in his favor on a legally inadequate theory, he cannot urge a wholly new theory on appeal to support *608that verdict. Federal Insurance Co. v. Bonilla Colon, 392 F.2d 662, 664-65 (1st Cir. 1968). Although Federal Insurance involved an attempt to argue on appeal a theory that plaintiff had affirmatively excluded below, we think that the same rule must apply when, through misdirected effort or a lack of preparation, plaintiff simply fails to present the proper law to the court and the jury. The result is a jury verdict that may or may not reflect findings of fact necessary for the theory argued on appeal — a jury verdict in which plaintiff can find no solace.
Affirmed.